Effectiveness of an inactivated Covid-19 vaccine with homologous and heterologous boosters against Omicron in Brazil

This study investigates the effectiveness of COVID-19 vaccine boosters following a primary series of CoronaVac vaccination. Using data from Brazil during the Omicron wave, the authors show that boosters provided protection against severe disease, with higher effectiveness from a BNT162b2 than CoronaVac booster. 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.

Automated summary

This study investigates the effectiveness of COVID-19 vaccine boosters following a primary series of CoronaVac vaccination. The study shows that boosters provide protection against severe disease, with higher effectiveness from a BNT162b2 booster compared to a CoronaVac booster. The study estimates the vaccine effectiveness (VE) of homologous and heterologous (BNT162b2) booster doses in adults who received two doses of CoronaVac in Brazil during the Omicron wave. The results indicate a VE of 8.6% for symptomatic disease and 56.8% for severe COVID-19 after receiving a homologous booster, while the VE for symptomatic disease is 56.8% and for severe COVID-19 is 86.0% after receiving a heterologous booster. Waning effectiveness against severe COVID-19 is observed only after 120 days in individuals who received a homologous booster. Heterologous boosters might be preferable for individuals who have completed a primary series of inactivated vaccines.