RESUMO
BackgroundThe rapid rise of Sars-Cov2 B.1.1.529 variant (named Omicron) in the late November 2021 prompted the health authorities to estimate the potential impact on the existing countermeasures, including vaccines. This meta-analysis aims to assess the effectiveness of the current Sars-Cov2 vaccine regimens against laboratory-confirmed Omicron infection. A secondary endpoint aims to investigate the waning effectiveness of primary vaccination against symptomatic Omicron infection and related hospitalization. MethodsThe systematic review started on December 1, 2021 and was concluded on March 1, 2022. Random-effects (RE) frequentist meta-analyses are performed to estimate the primary vaccination course and the booster dose effectiveness against Omicron. Multiple meta-regressions are performed under mixed-effects model. This study is registered with PROSPERO, CRD42021240143. FindingsIn total, 15 out of 502 records are included in the quantitative synthesis. The meta-analysis on B.1.1.529 infection risk produces an OR=0{middle dot}69 (95%CI: 0{middle dot}57 to 0{middle dot}83; {tau}2=0{middle dot}225; I2=99{middle dot}49%) after primary vaccination and an OR=0{middle dot}30 (95%CI: 0{middle dot}23 to 0{middle dot}39; {tau}2=0{middle dot}469; I2=99{middle dot}33%) after one additional booster dose. According to the multiple meta-regression models, one booster dose significantly decreases by 69% the risk of symptomatic Omicron infection (OR=0{middle dot}31; 95%CI: 0{middle dot}23 to 0{middle dot}40) and by 88% the risk of hospitalization (OR=0{middle dot}12; 95%CI: 0{middle dot}08 to 0{middle dot}19) with respect to unvaccinated. Six months after primary vaccination, the average risk reduction declines to 22% (OR=0{middle dot}78; 95%CI: 0{middle dot}69 to 0{middle dot}88) against symptomatic infection and to 55% against hospitalization (OR=0{middle dot}45; 95%CI: 0{middle dot}30 to 0{middle dot}68). InterpretationDespite the high heterogeneity, this study confirms that primary vaccination does not provide sufficient protection against symptomatic Omicron infection. Although the effectiveness of the primary vaccination against hospitalization due to Omicron remains significantly above 50% after 3 months, it dramatically fades after 6 months. Therefore, the administration of one additional booster dose is recommended within 6 months and provides a 76% decrease in the odds of symptomatic Omicron after five months. FundingThere was no funding source for this study. ARTICLE HIGHLIGHTSO_LIthe primary vaccination decreases the risk of Omicron infection by 31%, while one additional booster dose decreases the risk by 70% C_LIO_LIthe primary vaccination course reduces the risk of symptomatic Omicron infection by 24% and the risk of hospitalization by 50% C_LIO_LIone additional booster dose decreases by 69% the risk of symptomatic Omicron infection and the risk of hospitalization by 88% C_LIO_LIthe effectiveness of the primary vaccination against hospitalization dramatically wanes after 3 months from vaccination, reaching a minimum of 45% in risk reduction after more than 6 months C_LI PANEL: research in contextO_ST_ABSEvidence before this studyC_ST_ABSOmicron variants higher transmissibility combined with an increased risk of infection among individuals vaccinated with primary vaccination have prompted health authorities to introduce a booster vaccination. The systematic review including "vaccine effectiveness", "Covid-19", "SARS-CoV-2", and "Omicron" search terms, is performed over three web engines and one early stage research platform (i.e., WHO COVID-19 DATABASE, PubMed, medRxiv + bioRxiv) Additionally, all relevant web sources reporting living data on vaccine effectiveness (i.e., https://view-hub.org/covid-19/ and https://covid-nma.com/), electronic databases and grey literature are considered. The last search update was on March 1, 2022. No country, language, study design restrictions are applied. Added value of this studyPrimary vaccination provides relatively low protection against the Omicron VOC, while one additional booster dose decreased substantially the risk of symptomatic Omicron infection and of hospitalization. Implications of all the available evidenceThe booster dose should be recommended after three months and no later than six months after the primary course vaccination, in order to avoid severe consequences, in particular among the elderly population.
RESUMO
The SARS-CoV-2 variant of concern Omicron was first detected in Italy in November 2021. Data from three genomic surveys conducted in Italy between December 2021 and January 2022 suggest that Omicron became dominant in less than one month (prevalence on January 3: 78.6%-83.8%) with a doubling time of 2.7-3.1 days. The mean net reproduction number rose from about 1.15 in absence of Omicron to a peak of 1.83 for symptomatic cases and 1.33 for hospitalized cases, while it remained stable for critical cases.
RESUMO
SARS-CoV-2 variants of concern (B.1.1.7, P.1 and B.1.351) have emerged in different continents of the world. To date, little information is available on their ecological interactions. Based on two genomic surveillance surveys conducted on February 18 and March 18, 2021 across the whole Italian territory and covering over 3,000 clinical samples, we found significant co-circulation of B.1.1.7 and P.1. We showed that B.1.1.7 was already dominant on February 18 in a majority of regions/autonomous provinces (national prevalence 54%) and almost completely replaced historical lineages by March 18 (dominant in all regions/autonomous provinces, national prevalence 86%). At the same time, we found a substantial proportion of cases of the P.1 lineage on February 18, almost exclusively in Central Italy (with an overall prevalence in the macro-area of 18%), which remained at similar values on March 18, suggesting the inability by this lineage to outcompete B.1.1.7. Only 9 cases from variant B.1.351 were identified in the two surveys. At the national level, we estimated a mean relative transmissibility of B.1.1.7 (compared to historical lineages) ranging between 1.55 and 1.57 (with confidence intervals between 1.45 and 1.66). The relative transmissibility of P.1 estimated at the national level varied according to the assumed degree of cross-protection granted by infection with other lineages and ranged from 1.12 (95%CI 1.03-1.23) in the case of complete immune evasion by P.1 to 1.39 (95%CI 1.26-1.56) in the case of complete cross-protection. These observations may have important consequences on the assessment of future pandemic scenarios.
RESUMO
Vaccination campaigns against COVID-19 are allowing the progressive release of physical distancing restrictions in many countries. However, the global spread of the highly transmissible Delta variant has likely suppressed the residual chances of SARS-CoV-2 elimination through herd immunity alone. Here we assess the impact of the vaccination program in Italy since its start on December 27, 2020 and evaluate possible prospects for reopening the society while at the same time keeping COVID-19 under control. To this aim, we propose a mathematical modeling framework where levels of social activity are adjusted to match the time-series of the net reproduction number as estimated from surveillance data. We compared the estimated level of social contacts, number of deaths, and transmission potential with those of a counterfactual scenario where the same epidemic trajectory is obtained in absence of vaccination. We then evaluate the prospective impact of different scenarios of vaccination coverage and different social activity levels on SARS-CoV-2 reproduction number. We estimate that by June 30, 2021, the COVID-19 vaccination program allowed the resumption of about half the social contacts that were recorded in pre-pandemic times; in absence of vaccination, only about one third could have been resumed to obtain the same number of cases, with the added cost of about 12,100 (95%CI: 6,600-21,000) extra deaths (+27%; 95%CI: 15-47%) between December 27, 2020 and June 30, 2021. We show that the negative effect of the Delta variant diffusion in July was entirely offset by vaccination in the month of July and August 2021. Finally, we estimate that a complete return to the pre-pandemic life could be safely attained only if >90%, including children from 5 years on, will be vaccinated using mRNA vaccines developed in 2020. In any case, increasing the vaccination coverage will allow further margins for societal reopening even in absence of a pediatric vaccine. These results may support the definition of vaccination targets for countries that have already achieved a broad population coverage.
