Receiving a booster dose of Pfizer vaccine after two doses of CoronaVac produces more effective protection against the Ômicron variant than a third application of CoronaVac, indicates a study released today (5) by the Oswaldo Cruz Foundation (Fiocruz).
The study evaluated data from the e-SUS, the Influenza Epidemiological Surveillance Information System (Sivep-Gripe) and the National Immunization Program (PNI). Data span from September 6, 2021 to March 10, 2022, and were divided into two periods, from September 6, 2021 to December 14, 2021, when the Delta variant was dominant in Brazil; and from December 25, 2021 to March 10, 2022, when there was greater circulation of the Ômicron variant.
To assess the effectiveness of the booster dose in people vaccinated with two doses of CoronaVac, three scenarios were designed. In the first, people who received the two doses of the vaccine produced at the Butantan Institute and who did not reinforce the immunization in the following six months were analyzed. The researchers calculated that the effectiveness of single doses against symptomatic infections during the period of greatest circulation of the Omicron variant was 8.1%, while protection against serious disease outcomes reached 57%.
In the second scenario, cases where people were also given a booster dose of CoronaVac were evaluated, which produced additional protection that the researchers considered limited. The effectiveness against symptomatic infections was 15%, and against severe cases, 71.3%.
The third scenario, in which the booster dose was with the Pfizer vaccine, showed the highest percentages of effectiveness: 56.8% against symptomatic infections and 85.5% against severe cases. In addition, the study showed that, 90 days after the booster dose, protection against severe cases did not drop, which was observed in the vaccination with three doses of CoronaVac.
The researchers say that the conclusions reinforce the guidance of the Ministry of Health that the booster dose should be primarily with vaccines with messenger RNA technology. The recommendation was published in a November 2021 technical note LINK 1. In Brazil, Pfizer’s immunizer is the only one with this technological platform.
The vaccines against covid-19 used in Brazil are from three different technological platforms. In addition to the messenger RNA vaccine (Pfizer), which contain synthetic RNA from SARS-CoV-2, there are also viral vector vaccines (AstraZeneca and Janssen), in which another virus is used as a vector to carry genetic information from the coronavirus, and the inactivated virus (CoronaVac), which contains the “dead” virus, unable to replicate.
