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

Abstract

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.

Fig. 1. Times series of Covid-19 cases and Covid-19 hospital admissions or deaths, variants of concern prevalence and vaccination coverage in Brazil from Sep 2021 to Apr 2022.

Daily prevalence of SARS-CoV-2 variants among genotyped isolates were obtained from the GISAID (global initiative on sharing avian influenza data) database (extraction on 09 May 2022), selecting samples from Brazil. Green represents Delta prevalence, pink area represents Omicron prevalence and grey area represents others. Second dose coverage includes a single dose of Ad26.COV2.S. MA—moving averages.

Fig. 2. Adjusted vaccine effective estimates of primary two-dose vaccination with CoronaVac and subsequent booster vaccination with CoronaVac and BNT162b2 compared to unvaccinated individuals, according to days since receiving the last vaccine dose.

a against symptomatic Covid-19 (n = 321,390 for Delta predominance period and n = 2,773,088 for Omicron predominance period). b against Covid-19 hospitalization or death (n = 37,844 for Delta predominance period and n = 71,614 for Omicron predominance period). Squares represent the vaccine effectiveness adjusted by age, sex, self-reported race, number of chronic comorbidities, previous symptomatic events notified to the surveillance system, municipality of residence, and RT-PCR/antigen test sample collection date. The error bars represent the 95% confidence interval of the adjusted vaccine effectiveness. Grey shaded area represents the adjusted vaccine effectiveness for the two doses of CoronaVac, green shaded area represents the adjusted vaccine effectiveness for the homologous (CoronaVac) booster dose and the red shaded area represents the adjusted vaccine effectiveness for the heterologous (BNT162b2) booster dose.