Effectiveness of CoronaVac, ChAdOx1 nCoV-19, BNT162b2, and Ad26.COV2.S among individuals with previous SARS-CoV-2 infection in Brazil: a test-negative, case-control study

Effectiveness of COVID-19 mRNA Vaccination in Preventing COVID-19–Associated Hospitalization Among Adults with Previous SARS-CoV-2 Infection — United States, June 2021–February 2022

“…Benefit of vaccination after previous SARS-CoV-2 infection was also indicated by an analysis of surveillance data from New York City that estimated approximately 50%–70% protection against hospitalization from reinfection ( 5 ). A case-control analysis using surveillance data from Brazil estimated 90% protection by 2 doses of Pfizer-BioNTech vaccine against hospitalization or death after reinfection ( 6 ); the high estimated VE might partly reflect recent vaccination in the context of potential decreased infection-induced immunity. The similar estimated benefit from 1 or 2 vaccine doses in preventing reinfection leading to hospitalization in the current study is consistent with evidence that vaccination elicits a more rapid immunologic response if preceded by a SARS-CoV-2 infection ¶¶¶ ( 7 ).…”

“…The findings in this report are subject to at least five limitations. First, underascertainment of vaccination status from available information would likely lead to an underestimation of VE, particularly if vaccinated control-patients were misclassified as unvaccinated; this might have led to lower estimated VE compared with similar analyses ( 5 , 6 , 9 ). Second, generalizability might be limited by incomplete data or by missing data from persons who do not seek health care; however, Cosmos data are broadly representative of the U.S. population ( 4 ).…”

Vaccination plus previous infection: protection during the omicron wave in Brazil

“…We found that vaccination provided additional protection to that induced by past infection during the gamma (P.1) and delta (B.1.617.2) variant waves of the pandemic in Brazil. 1 With the emergence of the omicron (B.1.1.529) variant, vaccine effectiveness appears to decay, 2 , 3 but protection in individuals who have been previously infected and vaccinated remains unknown. We analysed the effect of hybrid immunity in preventing infection and severe outcomes during circulation of the omicron variant in Brazil.…”

Protection conferred by vaccine plus previous infection (hybrid immunity) with vaccines of three different platforms during the Omicron variant period in Brazil

“…Therefore, understanding hybrid immunity (infection plus vaccination) is crucial to guide future vaccination policies. We have demonstrated that vaccination offered additional protection to that induced by an infection during the Gamma and Delta variants waves in Brazil 2 . With the emergence of the Omicron variant, vaccine effectiveness (VE) appears to decay 3,4 , but the protection in previously infected vaccinees remains unknown.…”

“…Using national databases, we performed a test-negative case-control study as previously described 2 . Cases and controls were defined as individuals with RT-PCR/Lateral-flow tests positive or negative, respectively, between January 01 and March 22, 2022, a period of predominant circulation of the Omicron variant in Brazil (Appendix:pg=3-4).…”