A booster dose with a messenger RNA vaccine (such as Pfizer or Moderna) to a person who has been immunized with CoronaVac (from Sinovac, the Chinese vaccine) offers a considerably superior protection against covid-19 compared to booster with the same vaccine. In fact, two doses of CoronaVac provide protection almost nil. A observational study conducted in Brazil and co-directed by Fiocruz and the Barcelona Institute for Global Health (ISGlobal), a center supported by the “la Caixa” Foundation, follows up on those immunized with inactivated (killed) virus vaccines, such as CoronaVac.
To date, most studies on vaccine efficacy have focused on the adenoviral and messenger RNA vaccines, despite the widespread use of inactivated virus vaccines.especially in developing countries. low and middle income. In fact, half of the doses administered globally until January 2022 correspond to inactivated virus vaccines (CoronaVac and Sinopharm). Many experts have already expressed their doubts at the time about the efficacy of CoronaVac, which was much lower than that of vaccines marketed in Europe. ISGlobal’s research, published in the journal ‘Nature Communications’, has important implications for targeting reinforcement strategies in countries where the majority of the population received inactivated virus vaccines.
“Knowing the efficacy of the booster dose in populations vaccinated with inactivated virus is critical to guide the future vaccination strategies in these countries,” says Otavio RanzaniISGlobal researcher and first author of the study. Ranzani explains to this newspaper that “CoronaVac is used in more than 50 countries, including Asia, South America, Central America and Eastern Europe”. It is, per se, the “most widely used” vaccine. The covid-19 vaccination has been shown to be highly effective in protecting against severe disease and death. However, the efficacy of primary vaccination (i.e., the initial two doses) was diminished with the advent of new variantsespecially the omicron, which justified the need to administer a booster dose.
1.4 million cases
In this study, Ranzani and his colleagues evaluated the efficacy of booster with a CoronaVac vaccine or with a Pfizer vaccine. in Brazilian adults who initially received two doses of CoronaVac. The analysis, which included almost 1.4 million cases (with their respective control), was performed between December 2021 and April 2022, a time when omicron BA.1 was predominant, and compared to a period when delta was dominant. Brazil has used the vaccines CoronaVac, Astrazeneca, Pfizer and Janssen. The study describes the first eight months of the campaign in this country.
“The strength of our observational study is the. large sample size and the geographical coveragewhich covers each of Brazil’s 5,570 municipalities,” says Julio Crodaa researcher at Fiocruz and the Yale School of Public Health, and co-lead author of the study.
The results show that primary vaccination with two doses of CoronaVac offered almost no protection. against symptomatic omicron disease and 40% to 50% protection against severe disease. One dose of CoronaVac booster did not provide additional protection. against symptomatic disease, and only moderate protection against severe disease (74% and between 40% and 50% in those over 75 years of age). Moreover, this protection appears to decrease after four months. In contrast, the messenger RNA booster provided greater protection. against symptomatic and severe disease (56.8% and 86%, respectively) that appears to last more than four months.
“Our findings have immediate implications for the Reinforcement management strategies in the context of omicron-variant“, Ranzani states. They demonstrate that, in individuals who initially received inactivated vaccines, the booster with a messenger RNA vaccine provides a considerable increase in protection, even in the elderly.