RÉSUMÉ
The effectiveness of inactivated vaccines (VE) against symptomatic and severe COVID-19 caused by omicron is unknown. We conducted a nationwide, test-negative, case-control study to estimate VE for homologous and heterologous (BNT162b2) booster doses in adults who received two doses of CoronaVac in Brazil in the Omicron context. Analyzing 1,386,544 matched-pairs, VE against symptomatic disease was 8.6% (95% CI, 5.6-11.5) and 56.8% (95% CI, 56.3-57.3) in the period 8-59 days after receiving a homologous and heterologous booster, respectively. During the same interval, VE against severe Covid-19 was 73.6% (95% CI, 63.9-80.7) and 86.0% (95% CI, 84.5-87.4) after receiving a homologous and heterologous booster, respectively. Waning against severe Covid-19 after 120 days was only observed after a homologous booster. Heterologous booster might be preferable to individuals with completed primary series inactivated vaccine.
RÉSUMÉ
We used a test-negative design to estimate the vaccine effectiveness of Ad26.COV2.S (Janssen) against symptomatic COVID-19 and clinical outcomes in Mato-Grosso do Sul, Brazil. We analyzed 11,817 RT-PCR tests. The mean age was 37 (SD=17) years, 2,308 (20%) of individuals more or equal than 50 years and almost two-thirds of the population was Brown/Pardo. Adjusted effectiveness against symptomatic COVID-19 after 28 days of the single dose was 50.9% (95% CI, 35.5-63.0). Adjusted effectiveness against clinical outcomes was 72.9% (95% CI, 35.1-91.1) for hospitalization, 92.5% (95% CI, 54.9-99.6) for ICU admission, 88.7% (95% CI, 17.9-99.5) for mechanical ventilation and 90.5% (95% CI, 31.5-99.6) for death. Despite lacking precision on some estimates, a single dose of Ad26.COV2.S vaccine continues to protect specially for severe forms of COVID-19 in the context of new variants.