1. Introduction
The Omicron variant (B.1.1.529) was reported to the World Health Organization (WHO) from South Africa in late November 2021 [1]. It was immediately designated as a variant of concern (VOC) [1]. Compared to pre-omicron variants, a number of mutations have been identified in the omicron variant, including multiple mutations in the receptor-binding domain of the spike protein associated with increased transmissibility and immune evasion after natural infection and vaccination [2,3,4]. The omicron variant has rapidly evolved into new sub-lineages or sub-variants: BA.1 (B.1.1.529.1), BA.2 (B.1.1.529.2), BA.3 (B.1.1.529.3), BA.4 (B.1.1.529.4), and BA.5 (B.1.1.529.5). As of 29 November 2022, BA.5, BA.2.75, BA.4.6 and XBB (a hybrid of two different Omicron BA.2 sub-variants) are Omicron sub-lineages being monitored by the WHO to investigate if these lineages may pose an additional threat to global public health [1].
Several studies have shown diminished neutralization of both Omicron variants by pre-Omicron convalescent sera and by sera of vaccinated individuals [4,5,6]. Recent studies have shown a reduction in COVID-19 vaccine effectiveness against the Omicron variant [7,8,9,10,11], affecting the current COVID-19 vaccination strategy. Recent social media analysis has shown increased public vaccine hesitancy due to the potential lack of effectiveness of ancestral COVID-19 vaccines against the new VOCs [12].
Emerging data on high prevalence of asymptomatic infection, greater risk of reinfection, and reduced vaccine protection during the omicron-dominant period compared to the earlier VOC warrants further investigation on the effectiveness of current COVID-19 vaccines against the Omicron variant [7,8,9,10,11,13]. A systematic review and meta-analysis have recently been published to evaluate the effectiveness of the current COVID-19 vaccines against Omicron infection [14]. This meta-analysis included 15 studies and demonstrated that primary vaccination does not provide sufficient protection against symptomatic Omicron infection [14]. However, the systematic review included studies conducted in the early Omicron era with shorter-term follow up. The real-world long-term effectiveness and durability of protection conferred by primary COVID-19 vaccination course and booster doses against the Omicron variant is not precisely known. To summarize the existing evidence on the effectiveness and the duration of protection conferred by COVID-19 vaccines, data were synthesized from an ongoing systematic review [15]. This systematic review aimed to investigate the real-word effectiveness of primary and booster vaccination against SARS-CoV-2 infection and severe COVID-19 disease due to laboratory-confirmed SARS-CoV-2 Omicron variant. The review also aimed to evaluate the duration of protection following full vaccination and booster doses.
2. Methods
The systematic review drew data from an ongoing systematic review that aimed to synthesis and evaluate the vaccine effectiveness (VE) of COVID-19 vaccines at preventing SARS-CoV-2 infections and severe COVID-19 disease in real-world settings. The systematic review followed the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guideline and was registered in the Prospective Register of Systematic Reviews (PROSPERO registration ID: CRD42022291375) [15].
2.1. Search Strategy
Systematic literature searches were performed on MEDLINE, PubMed, Embase and Cochrane Database of Systematic Reviews website on or before 1 August 2022 with no language restrictions. WHO COVID-19 DATABASE, pre-print severs (medRxiv, bioRxiv) and grey literature were searched. For preprint studies with several versions available, the most recent update published up to 1 August 2022 was included. Reviews and their references are examined for inclusion. Medical subject headings with the following search keywords were used: SARS-CoV-2 OR COVID-19 AND Vaccine OR Vaccination AND OR Vaccine effectiveness. The methods have been previously described in detail in the ongoing systematic review protocol [15] and full search strategies are available in Supplementary Material S1.
2.2. Study Selection
Observational (non-randomized) studies including cohort studies (prospective or retrospective), cross-sectional studies, case control including test-negative design (TND), regression discontinuity design studies, post-licensure observational studies that investigated the effectiveness of COVID-19 vaccines against documented, symptomatic, severe COVID-19 disease (defined as hospitalization, ICU admission, intubation or mechanical ventilation, or death) were included. COVID-19 cases were defined as being due to the Omicron variant infection, based on S target–negative results on PCR or whole-genome sequencing. VE studies that evaluated effectiveness of the primary vaccine course and booster vaccination compared to no vaccination were included. Outcomes of interest were VE against Omicron infection of “any type” (i.e., studies did not indicate underlying symptoms), “symptomatic COVID-19”, and “severe COVID-19” due to Omicron infection. We only included studies that evaluated VE ≥14 days after the primary vaccination course, and ≥7 days after the booster dose. No restrictions were applied to the age of participants, the types of vaccination, or the number of participants. Heterologous primary schedules were considered. Studies that did not report VE data or did not use any confounder adjustment strategies were excluded.
All the relevant records were screened by title and abstract. The retrieval results were screened with the help of Endnote and duplicate studies were eliminated. Potentially relevant publications underwent full-text examination and disagreements on eligibility were solved through discussion. The full texts suitable for the quantitative synthesis were collected in an excel spreadsheet for data extraction.
2.3. Data Extraction
Data were extracted by three (H.M., D.D.P.-T. and Z.Y.M.Y.) independent reviewers to identify eligible studies that met pre-specified inclusion criteria. The following information: study design, year of publication, country, age, population type, type of vaccines, time period post primary series or booster doses and study follow-up period, were extracted from the eligible studies. VE data were stratified according to SARS-CoV-2 vaccination course, ≥14 days after completion of the primary vaccination course and ≥7 days after receiving the first or second booster doses. Within each subgroup, the vaccination course was classified according to the vaccine type or technology. Duration of effectiveness of SARS-CoV-2 vaccines was assessed in intervals of three, six, and longer than six months after the primary vaccination series, whereas for the booster vaccination, shorter time intervals were considered (seven or more days, within three months, three to six months) due to less follow-up time since introduction.
2.4. Quality Assessment
The Joanna Briggs Institute (JBI) tools [16] were used to assess risk of bias of the included studies (Supplementary Material S2).
2.5. Data Analysis
Descriptive statistics were used to summarize the characteristics of studies included in this review. VE was quantified as the risk reduction of any or severe Omicron infection, expressed as a percentage, compared to the unvaccinated group. VE estimates were derived from regression models (Logit, Poisson, and Cox regression models) and calculated as (1 − IRR) × 100, where IRR = incidence rate ratio; (1 − HR) × 100, where HR = Hazard ratio; (1 − RR) × 100, where RR = Risk ratio; and (1 − OR) × 100, where OR = Odds ratio is the ratio of the rate of COVID-19 in the vaccinated group to the corresponding rate in the unvaccinated group. The DerSimonian-Laird random-effects model with Hartung- Knapp-Sidik-Jonkman variance correction was used to combine VE estimates. We used the I2 test to quantify the heterogeneity between studies. I2 values were defined as low (≤50%), moderate (50–75%), or high heterogeneity (>75%). To estimate the duration of protection following the primary vaccination series, we modeled days since completing the primary course as a continuous effect, allowing for nonlinearity by using restricted cubic splines. The analysis was carried out using Stata 17.
3. Results
3.1. Characteristics of Studies
The initial search generated 13,601 studies. After removing duplicates, screening titles and abstracts of 7710 potential studies, 909 studies were identified for full text review (Figure 1). After a full text review, 299 studies were included for the ongoing systematic review as of 1 August 2022. In total, 28 observational VE studies on confirmed Omicron cases (22 case-control [9,10,11,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35] and six cohort studies [7,8,36,37,38,39]) were included in this meta-analysis. Overall, 17 studies [17,18,19,20,21,22,24,25,26,27,28,29,31,34,35,38,39] investigated VE of both primary and booster vaccination, nine primary vaccination course without boosters [7,8,9,11,23,32,36] and two evaluated VE of booster doses only [30,37]. A total of 238 different VE estimates against documented Omicron infection (n = 47), symptomatic (n = 95) and severe COVID-19 disease (n = 96) over different time periods were included in this meta-analysis. Of these, 47% (n = 112) were for primary vaccination series and 52.9% (n = 126) for booster doses. Of the total 238 VE estimates, 196 (82.2%) were calculated from odds ratio (OR), 29 (12.1%) from the hazard ratio (HR), 10 (4.2%) from incidence rate ratio (IRR) and three (1.2%) from risk ratio (RR).
The included studies had a total of sample size of 11.6 million individuals, and ranged from 1052 to 2,706,008 participants. The majority of the studies were carried out in USA (n = 12) [9,10,17,26,28,29,30,31,35,36,37,39] followed by the UK (n = 6) [11,25,32,33,34,38], Canada (n = 4) [19,20,21,24], Qatar (n = 2) [18,22], France (n = 1) [27], Denmark (n = 1) [7], South Africa (n = 1) [23] and Chile (n = 1) [8] (Table 1). The majority of the included studies (n = 18) evaluated VE in adults ≥18 years of age, while two were exclusively on the pediatric populations (5–12 years of age) [22,23], two on adolescents (12–17 years of age) [11,19], one middle age adults (40–64 years of age) [25] and two on older adults (≥60 years of age) [7,24]. Two studies [37] included high risk populations (patients under hemodialysis therapy). The primary vaccination course represents two doses of BNT162b2 (Pfizer–BioNTech), mRNA-1273 vaccines (Moderna), AZD1222 (ChAdOx1 nCoV-19, AstraZeneca), CoronaVac (Sinovac), or one dose of Ad26.COV2.S (Janssen) vaccines. Most booster studies investigated VE of a single mRNA-based booster dose following the primary vaccination course, and only one study reported VE of a third dose of the vector-based vaccine, AZD1222 [25]. One study evaluated the VE of a second booster dose of the mRNA-1273 vaccines following three doses of mRNA-based vaccines [24] (Table 1). The median follow-up period for booster dose was shorter (16.5 weeks, IQR: 8.5–24) compared to the primary vaccine course (44 weeks, IQR 24–48). The quality assessment of each study using the JBI critical appraisal checklist is listed in Supplementary Material S2. The majority of included VE studies accounted for key potential confounders that may have influenced both the receipt of COVID-19 vaccine and the occurrence of SARS-CoV-2 infection. The list of covariates used in final analyses of vaccine effectiveness (VE) estimates from the included primary studies is reported in Supplementary Material S3.
3.2. Vaccine Effectiveness
3.2.1. VE against Any Omicron Infection following Completion of the Primary Vaccination Course
A total of four studies (24 different VE estimates) [7,8,10,36] were included in the meta-analysis of primary vaccination series against Omicron infection. Two studies were conducted in the USA [10,36], one in Denmark [7] and one in Chile [8]. For all ages and vaccines, the pooled VE against any SARS-CoV-2 Omicron infection was 20.4% (95%CI: 12.1–28.7%, I2 = 96.4%). The pooled VE estimate within 3 months following the primary vaccination course was 28.1% (95 CI: 19.1–37.1%). The VE estimates varied based on vaccine type, for mRNA based; BNT162b2 38.1% (95%CI: 23.3–52.8%), mRNA-173, 27.8% (95%CI: 6.6–49.0%), BNT162b2 or mRNA-1273, 22.3 (95%CI: 8.6–36.0%) and for vector based; AZD1222, 9.4% (95%CI: −15.5–34.4%). The estimated VE for CoronaVac was 37.8% (95% CI: 36.1–39.6%, data from a single study) in children 3–5 years of age (Figure 2). As displayed on the scatter plot, VE against Omicron infection declined sharply approximately after 2 months (50–60 days) following the primary vaccination course (Figure S1). The pooled VE estimates decreased to 4.0% (95%CI −24.8–32.7%) within three to six months (only mRNA-based vaccines included). There were not enough time data points to estimate pooled VE against Omicron infection after six months (mRNA-1273; 5.9%, 95%CI: 0.60–11.2%, data from a single study) (Figure 2).
3.2.2. VE against Symptomatic Omicron Infection following Completion of the Primary Vaccination Course
A total of 10 studies (39 different VE estimates) were included in the meta-analysis of primary vaccination series against symptomatic Omicron infection conducted in the UK (n = 3) [11,25,32], Canada (n = 3) [19,20], Qatar (n = 2) [18,22], USA (n = 1) [9] and France (n = 1) [27]. The pooled VE estimate against symptomatic Omicron infection for all ages and vaccine types was 23.4% (95%CI: 13.5–33.3%, I2 = 99.6%). The pooled VE against symptomatic Omicron disease was 37.1% (95%CI: 26.9–47.2%) after the first three months, declining to 10.6% (95%CI: 4.6–16.5%) between three to six months to −4.3% (95%CI: −15.4–6.7%) after six months (Figure 3). VE against symptomatic Omicron infection had a similar reduction over time, rapidly declining around 40 days following the primary vaccination course, as shown on the scatter plot (Figure 4).
3.2.3. VE against Severe Omicron Infection following Completion of the Primary Vaccination Course
A total of 12 studies (49 different VE estimates) conducted in USA (n = 4) [17,28,29,31], Canada (n = 3) [19,20,24], Qatar (n = 2) [18,22], France (n = 1) [27], South Africa (n = 1) [23] and Chile (n = 1) [8] evaluated VE against severe Omicron infection. Severe COVID-19 was a composite outcome of hospitalization (59.1%), emergency department (14.2%), intubation or mechanical ventilation (14.2%), admission to the intensive care unit (ICU) (6.1%), or death (6.1%). Only two [27,35] studies evaluated the effectiveness of COVID-19 vaccines against death. Two studies [18,24] included death or hospitalization as a composite outcome of severe Omicron infection. Therefore, VE estimates against death were not pooled separately due to the low number of studies and insufficient data. The pooled VE against severe COVID-19 was 56.9% (95%CI: 51.4–62.5%, I2 = 84.4%) (Figure 5). VE against severe Omicron infection decreased from 63.6% (95%CI: 57.5–69.7%) at three months to 48.3% (95%CI: 39.0–57.6%) at six months following the primary vaccination series (Figure 5). VE remained stable after six months at 49.7% (95%CI: 35.7–63.7%), also shown on the scatter plot (Figure S2). The highest pooled VE estimates against severe Omicron disease were observed following two doses of mRNA-1273 within 3 months (72.5%, 95%CI: 55.7–89.3%, I2 = 59.7).
3.2.4. VE against Omicron Infection after the First Booster Dose
A total of eight studies conducted in the USA (n = 4) [31,35,37,39], Canada (n = 2) [21,24] and UK (n = 2) [34,38] evaluated VE (17 different VE estimates) [34,38] against Omicron infection. The overall pooled VE estimate of the first booster dose against Omicron infection was 48.8% (95% CI: 42.0–55.6%, I2 = 97.3%) (Figure 6). The pooled VE estimates of the first booster dose after 7–14 days was 41.4% (95%CI: 32.4–503%, I2 = 79.8%) and increased to 51.2% (95%CI: 43.9–58.6%) within three months following three doses of any mRNA vaccines. Data from a single study during the same time period showed a slightly lower VE estimates of 47% (95%CI: 13–81%) following two dose adenovirus vector vaccines with one mRNA vaccine (Figure 6). There was insufficient follow-up period post three months to evaluate the waning of booster vaccination against Omicron infection.
3.2.5. VE against Symptomatic Infection after the First Booster Dose
A total of eight studies conducted across Canada (n = 4) [19,20,21,24], UK (n = 2) [25,33], France (n = 1) [27] and Qatar (n = 2) [18,22] evaluated VE of one booster dose (50 different VE estimates). The pooled VE of a booster dose against symptomatic infection was 55.9% (95%CI: 53.4–58.4%, I2 = 98.4) (Figure 7). The VE varied by vaccine types and technology. The pooled VE estimates of three doses of mRNA vaccine after 7–14 days was 58.4% (95%CI: 54.8–62.0%, I2 = 83.7%). VE of the first booster dose remained stable up to three months following three doses of any mRNA vaccines (56.1%, 95%CI: 50.9–61.3%) or three doses of adenovirus vector vaccines (60.2%, 95%CI: 55.0–65.5%). Slightly lower VE estimates were observed for heterologous boosting using 2-dose adenovirus vector vaccines with one mRNA vaccine (51.7%, 95%CI: 50.9–61.3%). Between the periods three to six months, pooled VE estimates reduced to 32.8% (95%CI: 16.9–48.8%), waning less pronounced for three-dose, homologous mRNA vaccination (Figure 7).
3.2.6. VE against Severe Omicron Infection after the First Booster Dose
A total of 11 studies (39 different VE estimates) conducted in the USA (n = 5) [17,26,28,29,30], Canada (n = 3) [20,21,24], Qatar (n = 2) [18,22] and France (n = 1) [27] evaluated VE against severe Omicron infection. The pooled VE estimate of the first booster dose against severe Omicron disease was 86.5% (95%CI: 84.4–88.6%, I2 = 90.0%). The pooled VE estimates at 7–14 days was 88.1% (95%CI: 85.0–91.2%), 85.1% (95%CI: 80.2–90.1%) within 3 months and 88.0% (95%CI: 80.7–91.2%) within three to six months (three doses of any mRNA vaccines representing most of the pooled VE estimates) (Figure 8).
3.2.7. VE of a Second Booster or Fourth Dose
One study evaluated the VE of a fourth dose (second booster dose) of mRNA-1273 in older residents of long term care facilities in Ontario, Canada [24]. The pooled VE estimate of a fourth dose of mRNA-1273 followed by any combination of three mRNA vaccines at “≈7 days” against Omicron infection was 50.3% (95%CI: 47.1–53.6%), 69.7% (95%CI: 65.3–74.2%) against symptomatic Omicron infection, and 86% (95%CI: 81–90%) against severe outcomes (Figures S3–S5). There was no VE data for other time periods.
3.3. Subgroup Analyses
Subgroup VE analyses were performed by age, and sub-lineage of Omicron. For some subgroup analyses, there were not enough data points to estimate VE or duration of protection at different time points.
3.4. VE by Age Groups
3.4.1. Pediatric population
The pooled VE estimate for primary vaccination series (CoronaVac or BNT162b2) against Omicron infection in children under 12 years of age was 37.8% (95%CI: 36.0–39.5%) (Figure S6).
3.4.2. Adolescents
The pooled VE against Omicron infection following a two-dose BNT162b2 was 59.3% (95%CI: 40.7–77.9%) (Figure S6) and 49.7% (95%CI: 29.9–69.4%) against symptomatic infection in adolescents aged 12–18 years of age (Figure S7).
3.4.3. Middle Aged Adults
One study reported VE (8%; 95%CI: 6.0–9.9%) of symptomatic infection in middle aged adults 40–64 (Figure S7) [25]. The pooled VE against symptomatic Omicron infection for a primary series plus one booster of mRNA vaccine or AstraZeneca vaccine dose was 47.4% (95%CI: 23.3–71.5%) (Figure S8).
3.4.4. Older Adults
We observed a trend towards lower VE in the older age group (≥60 years of age). The pooled VE against any documented Omicron infection in older individual’s ≥ age 60 year was −6.9% (95%CI: −51.9–38.1%) following any two primary mRNA doses (BNT162b2 or mRNA-1273) (Figure S9). The pooled VE estimated for the first three months was 30.3 (95%CI: −10.0–70.7%) and substantially reduced to −58.2% (95%CI: −94.7–21.8%) within three to six months (Figure S10). There were not enough time data points to estimate VE longer than six months. Primary vaccination plus one booster dose of either the BNT162b2 or mRNA-1273 vaccines restored the protection to 57.9% (95%CI: 53.4–62.4%) within 3 months, and declined to 14.7% (95%CI: −22.0–51.5%) at six months (Figure S11). The pooled VE against severe infection following primary vaccine series was 58.5% (95%CI: 50.0–66.9%) (Figure S12) and increased to 81.6% (95%CI: 75.5–87.6%) following administration of one booster dose of mRNA or Vector vaccine (Figure S12). VE of the first booster dose against severe infection was 83.0% (95%CI: 76.0–90.0%) after ≥7 days and remained stable at 3 months (78.4%, 95%CI: 73.6–83.2%) (Figure S13). VE of the second booster dose against severe COVID-19 illness was estimated to be 86.8% as discussed above (Figure S5).
3.5. VE by Omicron Sub Linages
Only two studies reported VE for Omicron sub linages BA.1 [26] and BA.2 [21], whilst four studies [18,21,22,29] evaluated 26 different VE estimates against symptomatic Omicron infection by sub linages BA.1 and BA.2. Therefore, stratified meta-analysis on VE was only conducted for the latter. The primary series provided similar pooled VE against symptomatic Omicron BA.1 infection (11.3%, 95%CI: −11.3–33.8%) and BA.2 infection (15.1%, 95%CI: −10.2–40.3%) (Figure S14). VE of the first booster dose against symptomatic Omicron BA.1 was slightly higher for BA.1 (53.2%, 95%CI: 45.6–60.8%) compared to BA.2 (49.3%, 95%CI: 50.0–57.6%) (Figure S15). Pooled VE against severe BA.1 Omicron infection for the primary series plus one booster dose of any mRNA vaccine was 87.4% (95%CI: 70.5–104.4%), and for a primary series alone was 52.7% (95%CI: 29.4–76.0%). Similarly, pooled VE against severe BA.2 infection following primary series was 52.5% (95%CI: 27.5–77.6%) and increased to 87.3% following one booster of mRNA vaccination (Figures S16 and S17).
Additionally, we performed sensitivity analyses by study designs (cohort or case-control) and statistical methods employed to estimate the VE (Logit, Poisson, and Cox regression models). These subgroup analyses did not reveal any meaningful differences to the overall VE findings against all outcomes (noting small numbers in some subgroups) (Data not shown).
4. Discussion
Our meta-analysis of 28 studies, which included nearly 11 million individuals, provides evidence on VE and duration of protection of COVID-19 vaccines against SARS-CoV-2 Omicron infection and severe COVID-19. Our data suggest that primary vaccination series are not sufficiently protective against the Omicron infection and protection wanes substantially over time from 28% at three months to 4% at six months. Similar trends were observed for symptomatic Omicron infection following full vaccination, broadly consistent with recent review findings [14,40,41]. The waning of primary COVID-19 vaccination course was less pronounced against severe Omicron disease, decreasing from 64% at three months to 49% after six months, consistent with recent findings [14,40,41].
Our meta-analysis suggests that first booster dose restores and provides additional protection for all outcomes. VE of the first booster dose against any (51%) or symptomatic (57%) Omicron infection remained moderate for at least 3 months. Although there was limited data for longer follow-up, VE of the first booster dose against symptomatic Omicron infection waned to 33% at six months, falling below the WHO’s minimal criteria of 50% when considering the outcomes of infection and symptomatic disease. This suggests the waning effect is also present for booster vaccination, consistent with recent studies conducted during the Omicron-dominant period [42,43,44]. However, our review suggests that protection against severe Omicron cases remained robust up to 86% after a single dose of booster for at least up to six months, corroborating recent findings [14,40,41].
Vaccine waning following booster vaccination was lower among the younger age group compared to the older adults aged ≥60 years. VE of the second booster dose against symptomatic Omicron infection declined more rapidly in older adults aged ≥60 years from 58% at three months to 14% at six months [24]. However, high level protection against severe disease still remained up to 78% for at least six months after the second booster dose in older adults, who are more vulnerable to severe COVID-19 outcomes. As of 28 November 2022, 68.5% of the world population have not received booster doses [45]. Future research should continue to evaluate the VE of booster vaccination with longer follow-ups to determine the duration of protection against the Omicron variant.
This meta-analysis had several limitations. The included studies were highly heterogeneous in terms of study populations, statistical approaches employed, definitions of symptomatic or severe COVID-19 used, analysed time points after vaccination, and vaccination schedules and regimes. All these factors may contribute to the discrepancy in our VE estimates and limit the generalizability of our results. Although the included studies made some sort of adjustments to their final VE estimates, not all accounted for important confounders, such as previous SARS-CoV-2 infection, underlying comorbidities, socio-economic parameters and COVID mitigation strategies.
5. Conclusions
This meta-analysis from a wide variety of study types, settings and populations demonstrates that primary COVID-19 vaccination courses were limited in preventing infections and severe disease caused by the SARS CoV-2 Omicron variant. Our review highlights the importance of booster doses for protection against Omicron infection and, more importantly, in providing high levels of protection against severe Omicron disease, particularly among the elderly population. Further research on the real-world performance of the existing vaccines including the new Omicron-specific vaccines is needed.
Conceptualization, H.M., B.W., M.M., P.H.A. and H.S.M.; literature search and review, H.M., D.D.P.-T. and Z.Y.M.Y.; data extraction, H.M., D.D.P.-T. and Z.Y.M.Y.; data analysis, H.M. and B.W.; writing—original draft preparation, H.M.; writing—review and editing, H.M., D.D.P.-T., Z.Y.M.Y., B.W., M.M., P.H.A. and H.S.M.; All authors have read and agreed to the published version of the manuscript.
Not applicable.
Not applicable.
All data generated from the study have been included in the manuscript. Data were obtained from the primary studies included in the review.
H.S.M. is an investigator on vaccine trials sponsored by the GSK group of companies, Pfizer, Sanofi, and Merck. H.S.M.’s, H.M.’s, B.W.’s, M.M.’s and P.H.A.’s institution receives funding for investigator-led studies from industry, including Pfizer and Sanofi Pasteur; H.S.M., H.M., B.W., M.M. and P.H.A. receive no personal payments from industry. D.D.P.-T. and Z.Y.M.Y. declare no conflict of interest.
Footnotes
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
Enlarge this image.Figure 2. VE estimates against SARS-CoV-2 infection of the Omicron variant after the primary course, by vaccine types and time intervals.
Enlarge this image.Figure 3. VE estimates against symptomatic Omicron infection after the primary course, by vaccine types and time intervals.
Enlarge this image.Figure 4. Scatterplot of VE against symptomatic Omicron infection plotted according to time from the primary vaccination.
Enlarge this image.Figure 5. VE estimates against severe COVID-19 due to Omicron infection after the primary course by vaccine types and time intervals.
Enlarge this image.Figure 6. VE estimates against SARS-CoV-2 infection of the Omicron variant after one booster dose by vaccine types and time intervals.
Enlarge this image.Figure 7. VE estimates against symptomatic Omicron infection after one booster dose by vaccine types and time intervals.
Enlarge this image.Figure 8. VE estimates against severe COVID-19 due to Omicron infection after one booster dose by vaccine types and time intervals.
Characteristics of the studies included in the meta-analysis.
| Study | Country | Study Design | Population/Age Group | Sample Size | Type of Primary Vaccines | Time Interval since Primary Series (Days) | Type of Booster Vaccines | Time Interval since Booster Dose (Days) | Outcomes | VE/100% |
|---|---|---|---|---|---|---|---|---|---|---|
| Adams et al. 2022 [ |
USA | Case-negative control | Hospitalized adults ≥18 years | 3181 | Ad26.COV2.S, mRNA-1273, |
14+ | Ad26.COV2.S, mRNA-1273, |
7+ | Hospitalization | 1-OR |
| Altarawneh et al. 2022 [ |
Qatar | Case-negative control | Individuals, all ages | 158,484 | mRNA-1273, |
14+ | mRNA-1273, |
7+ | Symptomatic infection, hospitalization/death | 1-OR |
| Buchan et al. 2022a [ |
Canada | Case-negative control | Adolescents 12–17 years | 29,855 | BNT162b2 | 7–59, 180+ | BNT162b2 | 7+ | Symptomatic infection, severe infection | 1-OR |
| Buchan et al. 2022b [ |
Canada | Case-negative control | General population ≥18 years | 134,435 | BNT162b2 | 7–59, 180+, 240+ | BNT162b2, mRNA-1273 | 7+ | Symptomatic infection, severe infection | 1-OR |
| Carazo et al. 2022 [ |
Canada | Case-negative control | Healthcare workers aged 18–59 | 37,732 | mRNA-1273, |
14+ | mRNA-1273, |
14+ | Documented infection, symptomatic infection | 1-OR |
| Chemaitelly et al. 2022 [ |
Qatar | Case-negative control | General population ≥5 years | 2,706,008 | mRNA-1273, |
30–90, 30–182, 212+ | mRNA-1273, |
14–30, 30+, 43+ | Symptomatic infection, severe infection | 1-OR |
| Collie et al. 2022 [ |
South Africa | Case-negative control | General population ≥5 years | 211,610 | BNT162b2 | 14+ | NA | NA | Hospitalization | 1-OR |
| Fowlkes et al. 2022 [ |
USA | Cohort | Children 5–11 years | 1052 | BNT162b2 | 14–149, 150+ | NA | NA | Documented infection | 1-OR |
| Grewal et al. 2022 [ |
Canada | Case-negative control | LTCF residents 60+ years | 13,654 | mRNA-1273, |
14+ | mRNA-1273, |
7+, 14–84 | Documented infection, symptomatic infection, hospitalization/death | 1-OR |
| Hansen et al. 2021 [ |
Denmark | Cohort | Older adults 60+ years | 41,684 | mRNA-1273, |
15–44, 105–164 | NA | NA | Documented infection | 1-HR |
| Jara et al. 2022 [ |
Chile | Cohort | Children 3–5 years | 490,064 | CoronaVac | 14+ | NA | NA | Documented infection, hospitalization, ICU admission | 1-HR |
| Kim et al. 2022 [ |
USA | Case-negative control | General population ≥18 years | 3847 | mRNA-1273, |
14–14, 150 | NA | NA | Symptomatic infection | 1-RR |
| Kirsebom et al. 2022 [ |
UK | Case-negative control | 759,450 Middle-Aged Adults 40–64 & 759,450 Older adults 65+ years | 166,720 | AZD1222 | 175+ | AZD1222, BNT162b2 | 7+, 14–34, 70–104, 105+ | Symptomatic infection, Hospitalization | 1-OR |
| Lauring et al. 2022 [ |
USA | Case-negative control | General population ≥18 years | 17,126 | mRNA-1273, |
14+ | mRNA-1273, |
7+ | Hospitalization | 1-OR |
| Lind et al. 2022 [ |
USA | Case-negative control | General population ≥5 years | 130,073 | mRNA-1273, |
14, 14–149, 150+ | NA | NA | Documented infection | 1-OR |
| Montez-Rath et al. 2022 [ |
USA | Cohort | Dialysis patients ≥18 years | 3576 | NA | NA | mRNA-1273, |
21+ | Documented infection | 1-RR |
| Powell et al. 2022 [ |
UK | Case-negative control | Adolescents 12–17 years | 617,259 | BNT162b2 | 14–34, 70+ | NA | NA | Symptomatic infection | 1-OR |
| Spensley et al. 2022 [ |
UK | Cohort | Haemodialysis patients ≥18 years | 1121 | BNT162b2, AZD1222 | 14+ | AZD1222, BNT162b2 | 14+ | Documented infection | 1-HR |
| Suarez Castillo et al. 2022 [ |
France | Case-negative control | General population ≥18 years | 761,744 | BNT162b2, AZD1222 | 0–30, 180+ | BNT162b2, AZD1222 | 8–14, 90+ | Documented infection, hospitalization, ICU admission, Death | 1-OR |
| Tartof et al. 2022a [ |
USA | Case-negative control | General population ≥18 years | 11,123 | BNT162b2, | 7–90 | BNT162b2 | 14–90, 90+ | Hospitalization, ED admissions | 1-OR |
| Tartof et al. 2022b [ |
USA | Case-negative control | General population ≥18 years | 65,813 | BNT162b2 | 14–182, 182+ | BNT162b2 | 7–90, 90+ | Hospitalization, ED admissions | 1-OR |
| Thompson et al. 2022 [ |
USA | Case-negative control | Hospitalized adults ≥18 years | 31,0676 | Not stated | Not stated | mRNA-1273, |
14+ | Hospitalization, ED admissions | 1-OR |
| Tseng et al. 2022 [ |
USA | Case-negative control | General population ≥18 years | 109,662 | mRNA-1273 | 14+, 14–90, 270+ | mRNA-1273 | 14+, 14–60 | Documented infection, hospitalization | 1-OR |
| UKHSA 2022 [ |
UK | Case-negative control | General population ≥18 years | 996,670 | BNT162b2, AZD1222, mRNA-1273 | 14–28, 140–168, 175+ | NA | NA | Symptomatic infection | 1-HR |
| UKHSA/Andrews et al. 2022 [ |
UK | Case-negative control | General population ≥18 years | 996,670 | Not stated | Not stated | BNT162b2, AZD1222, mRNA-1273 | 14–28, 29–53, 70+ | Symptomatic infection | 1-IRR |
| Willet et al. 2022 [ |
UK | Case-negative control | General population ≥18 years | 11,077 | mRNA-1273, |
14+ | mRNA-1273, |
14+ | Documented infection | 1-OR |
| Yoon et al. 2022 [ |
USA | Cohort | Healthcare workers ≥18 years | 3241 | mRNA-1273, |
14+ | mRNA-1273 | 7+ | Documented infection | 1-HR |
| Young-Xu et al. 2022 [ |
USA | Case-negative control | Veterans ≥18 years | 372,636 | mRNA-1273, |
14+ | mRNA-1273, |
14+ | Documented infection, hospitalization, death | 1-OR |
Supplementary Materials
The following supporting information can be downloaded at:
References
1. World Health Organization [WHO]. Tracking SARS-CoV-2 Variants. Available online: https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/ (accessed on 2 April 2022).
2. Pulliam, J.R.C.; van Schalkwyk, C.; Govender, N.; von Gottberg, A.; Cohen, C.; Groome, M.J.; Dushoff, J.; Mlisana, K.; Moultrie, H. Increased risk of SARS-CoV-2 reinfection associated with emergence of the Omicron variant in South Africa. medRxiv; 2021; [DOI: https://dx.doi.org/10.1101/2021.11.11.21266068]
3. Araf, Y.; Akter, F.; Tang, Y.D.; Fatemi, R.; Parvez, M.S.A.; Zheng, C.; Hossain, M.G. Omicron variant of SARS-CoV-2: Genomics, transmissibility, and responses to current COVID-19 vaccines. J. Med. Virol.; 2022; 94, pp. 1825-1832. [DOI: https://dx.doi.org/10.1002/jmv.27588] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35023191]
4. Bekliz, M.; Adea, K.; Vetter, P.; Eberhardt, C.S.; Hosszu-Fellous, K.; Vu, D.-L.; Puhach, O.; Essaidi-Laziosi, M.; Waldvogel-Abramowski, S.; Stephan, C. et al. Neutralization capacity of antibodies elicited through homologous or heterologous infection or vaccination against SARS-CoV-2 VOCs. Nat. Commun.; 2022; 13, 3840. [DOI: https://dx.doi.org/10.1038/s41467-022-31556-1] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35787633]
5. Cao, Y.; Wang, J.; Jian, F.; Xiao, T.; Song, W.; Yisimayi, A.; Huang, W.; Li, Q.; Wang, P.; An, R. et al. Omicron escapes the majority of existing SARS-CoV-2 neutralizing antibodies. Nature; 2022; 602, pp. 657-663. [DOI: https://dx.doi.org/10.1038/s41586-021-04385-3] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35016194]
6. Sullivan, D.J.; Franchini, M.; Joyner, M.J.; Casadevall, A.; Focosi, D. Analysis of anti-SARS-CoV-2 Omicron-neutralizing antibody titers in different vaccinated and unvaccinated convalescent plasma sources. Nat. Commun.; 2022; 13, 6478. [DOI: https://dx.doi.org/10.1038/s41467-022-33864-y] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36309490]
7. Hansen, C.H.; Schelde, A.B.; Moustsen-Helm, I.R.; Emborg, H.-D.; Krause, T.G.; Mølbak, K.; Valentiner-Branth, P. Vaccine effectiveness against SARS-CoV-2 infection with the Omicron or Delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: A Danish cohort study. medRxiv; 2021; [DOI: https://dx.doi.org/10.1101/2021.12.20.21267966]
8. Jara, A.; Undurraga, E.A.; Zubizarreta, J.R.; González, C.; Acevedo, J.; Pizarro, A.; Vergara, V.; Soto-Marchant, M.; Gilabert, R.; Flores, J.C. et al. Effectiveness of CoronaVac in children 3–5 years of age during the SARS-CoV-2 Omicron outbreak in Chile. Nat. Med.; 2022; 28, pp. 1377-1380. [DOI: https://dx.doi.org/10.1038/s41591-022-01874-4]
9. Kim, S.S.; Chung, J.R.; Talbot, H.K.; Grijalva, C.G.; Wernli, K.J.; Kiniry, E.; Martin, E.T.; Monto, A.S.; Belongia, E.A.; McLean, H.Q. et al. Effectiveness of 2 and 3 mRNA COVID-19 Vaccines Doses against Omicron and Delta-Related Outpatient Illness among Adults, October 2021–February 2022. medRxiv; 2022; [DOI: https://dx.doi.org/10.1111/irv.13029]
10. Lind, M.L.; Robertson, A.J.; Silva, J.; Warner, F.; Coppi, A.C.; Price, N.; Duckwall, C.; Sosensky, P.; Di Giuseppe, E.C.; Borg, R. et al. Effectiveness of Primary and Booster COVID-19 mRNA Vaccination against Omicron Variant SARS-CoV-2 Infection in People with a Prior SARS-CoV-2 Infection. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2022.04.19.22274056]
11. Powell, A.A.; Kirsebom, F.; Stowe, J.; McOwat, K.; Saliba, V.; Ramsay, M.E.; Lopez-Bernal, J.; Andrews, N.; Ladhani, S.N. Effectiveness of BNT162b2 against COVID-19 in adolescents. Lancet Infect. Dis.; 2022; 22, pp. 581-583. [DOI: https://dx.doi.org/10.1016/S1473-3099(22)00177-3]
12. Ng, Q.X.; Lim, S.R.; Yau, C.E.; Liew, T.M. Examining the Prevailing Negative Sentiments Related to COVID-19 Vaccination: Unsupervised Deep Learning of Twitter Posts over a 16 Month Period. Vaccines; 2022; 10, 1457. [DOI: https://dx.doi.org/10.3390/vaccines10091457] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36146535]
13. Garrett, N.; Tapley, A.; Andriesen, J.; Seocharan, I.; Fisher, L.H.; Bunts, L.; Espy, N.; Wallis, C.L.; Randhawa, A.K.; Ketter, N. et al. High Rate of Asymptomatic Carriage Associated with Variant Strain Omicron. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2021.12.20.21268130]
14. Meggiolaro, A.; Schepisi, M.S.; Farina, S.; Castagna, C.; Mammone, A.; Siddu, A.; Stefanelli, P.; Boccia, S.; Rezza, G. Effectiveness of vaccination against SARS-CoV-2 Omicron variant infection, symptomatic disease, and hospitalization: A systematic review and meta-analysis. Expert Rev. Vaccines; 2022; 21, pp. 1831-1841. [DOI: https://dx.doi.org/10.1080/14760584.2022.2130773] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36242513]
15. Mohammed, H.; Yeoh, Z.Y.M.; Nguyen, X.M.; Balanga, L.; Pham-Tran, D.; Marshall, H. A Systematic Review and Meta-Analysis on the Real-World Effectiveness of COVID-19 Vaccines. 2021; Available online: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=291375 (accessed on 16 March 2022).
16. Aromataris, E.; Fernandez, R.; Godfrey, C.M.; Holly, C.; Khalil, H.; Tungpunkom, P. Summarizing systematic reviews: Methodological development, conduct and reporting of an umbrella review approach. Int. J. Evid. Based Healthc.; 2015; 13, pp. 132-140. [DOI: https://dx.doi.org/10.1097/XEB.0000000000000055] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/26360830]
17. Adams, K.; Rhoads, J.P.; Surie, D.; Gaglani, M.; Ginde, A.A.; McNeal, T.; Ghamande, S.; Huynh, D.; Talbot, H.K.; Casey, J.D. et al. Vaccine effectiveness of primary series and booster doses against omicron variant covid-19-associated hospitalization in the united states. medRxiv; 2022; 2022.2006.2009.22276228. [DOI: https://dx.doi.org/10.1101/2022.06.09.22276228]
18. Altarawneh, H.N.; Chemaitelly, H.; Ayoub, H.H.; Tang, P.; Hasan, M.R.; Yassine, H.M.; Al-Khatib, H.A.; Smatti, M.K.; Coyle, P.; Al-Kanaani, Z. et al. Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections. N. Engl. J. Med.; 2022; 387, pp. 21-34. [DOI: https://dx.doi.org/10.1056/NEJMoa2203965]
19. Buchan, S.A.; Nguyen, L.; Wilson, S.E.; Kitchen, S.A.; Kwong, J.C. Vaccine effectiveness of BNT162b2 against Omicron and Delta outcomes in adolescents. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2022.04.07.22273319]
20. Buchan, S.A.; Chung, H.; Brown, K.A.; Austin, P.C.; Fell, D.B.; Gubbay, J.B.; Nasreen, S.; Schwartz, K.L.; Sundaram, M.E.; Tadrous, M. et al. Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes. medRxiv; 2022; [DOI: https://dx.doi.org/10.1001/jamanetworkopen.2022.32760]
21. Carazo, S.; Skowronski, D.M.; Brisson, M.; Barkati, S.; Sauvageau, C.; Brousseau, N.; Gilca, R.; Fafard, J.; Talbot, D.; Ouakki, M. et al. Protection against Omicron BA.2 reinfection conferred by primary Omicron or pre-Omicron infection with and without mRNA vaccination. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2022.06.23.22276824]
22. Chemaitelly, H.; Ayoub, H.H.; AlMukdad, S.; Coyle, P.; Tang, P.; Yassine, H.M.; Al-Khatib, H.A.; Smatti, M.K.; Hasan, M.R.; Al-Kanaani, Z. et al. Duration of mRNA vaccine protection against SARS-CoV-2 Omicron BA.1 and BA.2 subvariants in Qatar. Nat. Commun.; 2022; 13, 3082. [DOI: https://dx.doi.org/10.1038/s41467-022-30895-3]
23. Collie, S.; Champion, J.; Moultrie, H.; Bekker, L.-G.; Gray, G. Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa. N. Engl. J. Med.; 2021; 386, pp. 494-496. [DOI: https://dx.doi.org/10.1056/NEJMc2119270]
24. Grewal, R.; Kitchen, S.A.; Nguyen, L.; Buchan, S.A.; Wilson, S.E.; Costa, A.P.; Kwong, J.C. Effectiveness of a fourth dose of COVID-19 mRNA vaccine against the omicron variant among long term care residents in Ontario, Canada: Test negative design study. BMJ; 2022; 378, e071502. [DOI: https://dx.doi.org/10.1136/bmj-2022-071502]
25. Kirsebom, F.; Andrews, N.; Sachdeva, R.; Stowe, J.; Ramsay, M.; Bernal, J.L. Effectiveness of ChAdOx1-S COVID-19 Booster Vaccination against the Omicron and Delta variants in England. medRxiv; 2022; [DOI: https://dx.doi.org/10.1038/s41467-022-35168-7]
26. Lauring, A.S.; Tenforde, M.W.; Chappell, J.D.; Gaglani, M.; Ginde, A.A.; McNeal, T.; Ghamande, S.; Douin, D.J.; Talbot, H.K.; Casey, J.D. et al. Clinical severity of, and effectiveness of mRNA vaccines against, COVID-19 from omicron, delta, and alpha SARS-CoV-2 variants in the United States: Prospective observational study. BMJ; 2022; 376, e069761. [DOI: https://dx.doi.org/10.1136/bmj-2021-069761] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35264324]
27. Suarez, C.; Milena Khaoua, H.; Courtejoie, N. Vaccine-induced and naturally-acquired protection against Omicron and Delta symptomatic infection and severe COVID-19 outcomes, France, December 2021 to January 2022. Eurosurveillance; 2022; 27, 2200250. [DOI: https://dx.doi.org/10.2807/1560-7917.ES.2022.27.16.2200250]
28. Tartof, S.Y.; Slezak, J.M.; Puzniak, L.; Hong, V.; Xie, F.; Ackerson, B.K.; Valluri, S.R.; Jodar, L.; McLaughlin, J.M. Durability of BNT162b2 vaccine against hospital and emergency department admissions due to the omicron and delta variants in a large health system in the USA: A test-negative case–control study. Lancet Respir. Med.; 2022; 10, pp. 689-699. [DOI: https://dx.doi.org/10.1016/S2213-2600(22)00101-1]
29. Tartof, S.Y.; Slezak, J.M.; Puzniak, L.; Hong, V.; Xie, F.; Ackerson, B.K.; Valluri, S.R.; Jodar, L.; McLaughlin, J.M. BNT162b2 Effectiveness and Durability against BA.1 and BA.2 Hospital and Emergency Department Admissions in a Large US Health System: A Test-Negative Design. SSRN; 2022; [DOI: https://dx.doi.org/10.2139/ssrn.4150500]
30. Thompson, M.G.; Natarajan, K.; Irving, S.A.; Rowley, E.A.; Griggs, E.P.; Gaglani, M.; Klein, N.P.; Grannis, S.J.; DeSilva, M.B.; Stenehjem, E. et al. Effectiveness of a Third Dose of mRNA Vaccines against COVID-19-Associated Emergency Department and Urgent Care Encounters and Hospitalizations among Adults During Periods of Delta and Omicron Variant Predominance—VISION Network, 10 States, August 2021–January 2022. MMWR Morb. Mortal. Wkly. Rep.; 2022; 71, pp. 139-145. [DOI: https://dx.doi.org/10.15585/mmwr.mm7104e3] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35085224]
31. Tseng, H.F.; Ackerson, B.K.; Luo, Y.; Sy, L.S.; Talarico, C.A.; Tian, Y.; Bruxvoort, K.J.; Tubert, J.E.; Florea, A.; Ku, J.H. et al. Effectiveness of mRNA-1273 against SARS-CoV-2 Omicron and Delta variants. Nat. Med.; 2022; 28, pp. 1063-1071. [DOI: https://dx.doi.org/10.1038/s41591-022-01753-y]
32. UK Health Security Agency Andrews, N.; Stowe, J.; Kirsebom, F.; Toffa, S.; Rickeard, T.; Gallagher, E.; Gower, C.; Kall, M.; Groves, N. et al. COVID-19 Vaccine Effectiveness against the Omicron (B.1.1.529) Variant. N. Engl. J. Med.; 2022; 386, pp. 1532-1546. [DOI: https://dx.doi.org/10.1056/NEJMoa2119451]
33. UK Health Security Agency. SARS-CoV-2 Variants of Concern and Variants under Investigation in England Technical Briefing 34. Available online: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1050236/technical-briefing-34-14-january-2022.pdf (accessed on 9 July 2022).
34. Willett, B.J.; Grove, J.; MacLean, O.A.; Wilkie, C.; Logan, N.; Lorenzo, G.D.; Furnon, W.; Scott, S.; Manali, M.; Szemiel, A. et al. The hyper-transmissible SARS-CoV-2 Omicron variant exhibits significant antigenic change, vaccine escape and a switch in cell entry mechanism. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2022.01.03.21268111]
35. Young-Xu, Y.; Zwain, G.M.; Izurieta, H.S.; Korves, C.; Powell, E.I.; Smith, J.; Balajee, A.S.; Holodniy, M.; Beenhouwer, D.O.; Rodriguez-Barradas, M.C. et al. Effectiveness of mRNA COVID-19 Booster Vaccines against Omicron and Delta Variants among US Veterans. medRxiv; 2022; [DOI: https://dx.doi.org/10.1101/2022.01.15.22269360]
36. Fowlkes, A.L.; Yoon, S.K.; Lutrick, K.; Gwynn, L.; Burns, J.; Grant, L.; Phillips, A.L.; Ellingson, K.; Ferraris, M.V.; LeClair, L.B. et al. Effectiveness of 2-Dose BNT162b2 (Pfizer BioNTech) mRNA Vaccine in Preventing SARS-CoV-2 Infection among Children Aged 5–11 Years and Adolescents Aged 12–15 Years—PROTECT Cohort, July 2021–February 2022. MMWR Morb. Mortal. Wkly. Rep.; 2022; 71, pp. 422-428. [DOI: https://dx.doi.org/10.15585/mmwr.mm7111e1] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35298453]
37. Montez-Rath, M.E.; Garcia, P.; Han, J.; Cadden, L.; Hunsader, P.; Morgan, C.; Kerschmann, R.; Beyer, P.; Dittrich, M.; Block, G.A. et al. SARS-CoV-2 infection during the Omicron surge among patients receiving dialysis: The role of circulating receptor-binding domain antibodies and vaccine doses. medRxiv; 2022; [DOI: https://dx.doi.org/10.1681/ASN.2022040504]
38. Spensley, K.J.; Gleeson, S.; Martin, P.; Thomson, T.; Clarke, C.L.; Pickard, G.; Thomas, D.; McAdoo, S.P.; Randell, P.; Kelleher, P. et al. Comparison of Vaccine Effectiveness Against the Omicron (B.1.1.529) Variant in Hemodialysis Patients. Kidney Int. Rep.; 2022; 7, pp. 1406-1409. [DOI: https://dx.doi.org/10.1016/j.ekir.2022.04.005] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35434428]
39. Yoon, S.K.; Hegmann, K.T.; Thiese, M.S.; Burgess, J.L.; Ellingson, K.; Lutrick, K.; Olsho, L.E.W.; Edwards, L.J.; Sokol, B.; Caban-Martinez, A.J. et al. Protection with a Third Dose of mRNA Vaccine against SARS-CoV-2 Variants in Frontline Workers. N. Engl. J. Med.; 2022; 386, pp. 1855-1857. [DOI: https://dx.doi.org/10.1056/NEJMc2201821]
40. Zou, Y.; Huang, D.; Jiang, Q.; Guo, Y.; Chen, C. The Vaccine Efficacy against the SARS-CoV-2 Omicron: A Systemic Review and Meta-Analysis. Front. Public Health; 2022; 10, 940956. [DOI: https://dx.doi.org/10.3389/fpubh.2022.940956]
41. Külper-Schiek, W.; Piechotta, V.; Pilic, A.; Batke, M.; Dreveton, L.S.; Geurts, B.; Koch, J.; Köppe, S.; Treskova, M.; Vygen-Bonnet, S. et al. Facing the Omicron variant-how well do vaccines protect against mild and severe COVID-19? Third interim analysis of a living systematic review. Front. Immunol.; 2022; 13, 940562. [DOI: https://dx.doi.org/10.3389/fimmu.2022.940562]
42. Young-Xu, Y.; Zwain, G.M.; Izurieta, H.S.; Korves, C.; Powell, E.I.; Smith, J.; Balajee, A.; Holodniy, M.; Beenhouwer, D.O.; Rodriguez-Barradas, M.C. et al. Effectiveness of mRNA COVID-19 vaccines against Omicron and Delta variants in a matched test-negative case-control study among US veterans. BMJ Open; 2022; 12, e063935. [DOI: https://dx.doi.org/10.1136/bmjopen-2022-063935]
43. Arashiro, T.; Arima, Y.; Muraoka, H.; Sato, A.; Oba, K.; Uehara, Y.; Arioka, H.; Yanai, H.; Kuramochi, J.; Ihara, G. et al. COVID-19 vaccine effectiveness against symptomatic SARS-CoV-2 infection during Delta-dominant and Omicron-dominant periods in Japan: A multi-center prospective case-control study (FASCINATE study). Clin. Infect. Dis. Off. Publ. Infect. Dis. Soc. Am.; 2022; [DOI: https://dx.doi.org/10.1093/cid/ciac635]
44. Gram, M.A.; Emborg, H.D.; Schelde, A.B.; Friis, N.U.; Nielsen, K.F.; Moustsen-Helms, I.R.; Legarth, R.; Lam, J.U.H.; Chaine, M.; Malik, A.Z. et al. Vaccine effectiveness against SARS-CoV-2 infection or COVID-19 hospitalization with the Alpha, Delta, or Omicron SARS-CoV-2 variant: A nationwide Danish cohort study. PLoS Med.; 2022; 19, e1003992. [DOI: https://dx.doi.org/10.1371/journal.pmed.1003992]
45. Ritchie, H.; Ortiz-Ospina, E.; Beltekian, D.; Mathieu, E.; Hasell, J.; Macdonald, B.; Giattino, C.; Roser, M. Our World in Data- Coronavirus (COVID-19) Vaccinations. Available online: https://ourworldindata.org/covid-vaccinations (accessed on 28 November 2022).
© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.
Details
; Andraweera, Prabha H 1
; Marshall, Helen S 1 1 Vaccinology and Immunology Research Trials Unit, Women’s and Children’s Health Network, Adelaide, SA 5006, Australia; Robinson Research Institute and Adelaide Medical School, the University of Adelaide, Adelaide, SA 5006, Australia
2 Robinson Research Institute and Adelaide Medical School, the University of Adelaide, Adelaide, SA 5006, Australia