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

Using national COVID-19 notification, hospitalisation, and vaccination datasets from Brazil, we did a testnegative, case-control study to assess the effectiveness of four vaccines (CoronaVac [Sinovac], ChAdOx1 nCoV-19 [AstraZeneca], Ad26.COV2.S [Janssen], and BNT162b2 [Pfizer-BioNtech]) for individuals with laboratory-confirmed previous SARS-CoV-2 infection. We matched cases with RT-PCR positive, symptomatic COVID-19 with up to ten controls with negative RT-PCR tests who presented with symptomatic illnesses, restricting both groups to tests done at least 90 days after an initial infection. We used multivariable conditional logistic regression to compare the odds of test positivity and the odds of hospitalisation or death due to COVID-19, according to vaccination status and time since first or second dose of vaccines.

PRE-PRINT: The effectiveness of Vaxzevria and CoronaVac vaccines: A nationwide longitudinal retrospective study of 61 million Brazilians (VigiVac-COVID19)

Both  vaccines  demonstrated  overall  effectiveness  against  severe  COVID-19  up  to  80  years  of age.  Our  results  suggest  that  individuals  aged  90  years or  older  may  benefit from  an expedited  third  booster  dose.  Ongoing  evaluations, including  any  additional  vaccines authorized,  are  crucial  to  monitoring  long-term vaccine  effectiveness.

PRE-PRINT: Effectiveness of the CoronaVac Vaccine in Prevention of Symptomatic and Progression to Severe COVID-19 in Pregnant Women in Brazil

A complete regimen of CoronaVac in pregnant women was effective in preventing symptomatic Covid-19, and highly effective against severe illness in a setting that combines high disease burden and elevated Covid-19 related maternal deaths.

Influence of age on the effectiveness and duration of protection in Vaxzevria and CoronaVac vaccines

Background High rates of virus transmission and the presence of variants of concern can affect vaccine effectiveness (VE). Both conditions occur in low-income countries, which primarily use viral vector or inactivated virus vaccine technologies. Such countries conducted few VE analyses, and most lack the power to evaluate effectiveness in subgroups.