Cristina Azevedo (Fiocruz News Agency)
A comparison of elderly vaccination data with hospitalization and death records due to Severe Acute Respiratory Syndrome (SARS) or COVID-19 (confirmed or suspected) has shown the effectiveness of the two main immunizers used in Brazil in reducing severe cases and hospitalizations. This is indicated by a Technical Note from Fiocruz's COVID-19 Observatory, published this Friday (7/9). Entitled Analysis of the COVID-19 vaccination effectiveness in Brazil for hospitalization or death cases, the note evaluates individuals immunized with at least the first dose and those immunized with both doses. In the first case, regardless of the COVID-19 vaccine applied, the effectiveness was 73.7% in the 60- to 79-year-old age group and 63% among people over 80 years old.
Photo: Bernardo Portella
With at least the AstraZeneca/Oxford first dose, which in Brazil is produced by Fiocruz, an effectiveness rate of 81.7% was found in the 60-79 age group, and 62.8% in those over 80. With CoronaVac, the rate observed was 70.3% between 60 and 79 years of age, and 62.9% for those over 80.
With the full two-dose regimen, the effectiveness increases, regardless of the vaccine applied, to 79.8%, from 60 to 79 years old, and 70.3% over 80 years old. With AstraZeneca's two doses, an effectiveness rate of 93.8% was estimated from 60 to 79 years, and 91.3% over 80 years. Among those vaccinated with the two doses of CoronaVac, the rates were 79.6% from age 60 to 79, and 68.8% over age 80.
The efficacy of these vaccines has been demonstrated previously in their respective clinical studies. The Technical Note authors observe that one of the differentials of this study is to present vaccine effectiveness against variants of concern evidence that are prevalent in the Brazilian territory.
"Very high incidence rate values are observed in late February and early March, when a process of cases number decrease begins, being more expressive for age groups 60-79 years and 80+ years, "the note says. "With the vaccination effectiveness results described here and with vaccination coverage higher in these age groups than in others in the period, vaccination was an important factor in reducing the number of severe cases and deaths."
The study was conducted by statistical analysis using SI-PNI and Sivep-Gripe vaccination databases, linked by the National Immunization Program (NIP) staff. With data reported through June 7, the assessment involved total records of more than 40 million people vaccinated with at least one dose of vaccine and more than 798,000 severe cases or deaths, with COVID-19 confirmed or suspected SARS. The cases were differentiated between immunized and non-immunized, and further divided by age groups.
The study also shows that effectiveness is reduced for some age groups, particularly the elderly, aged 80 and over. According to the Note, "Immunosenescence [a set of changes that occur in the immune response according to aging] and a more limited duration of immunity in the 80+ group could also lead to lower effectiveness, given that this group had priority to start the immunization process earlier."
The group of researchers involved in the study states that the vaccination effectiveness will continue to be evaluated seeking to estimate the effectiveness data of the vaccines with their real-world use, in the epidemiology and circulating variants context. "The data obtained so far mainly reflect evidence of vaccine protection against the Gamma variant, prevalent in the country in this period. Other studies that follow the epidemiological profile and socio-demographic aspects of vaccinated and unvaccinated individuals will also be important," says the Technical Note.