COVID-19 vaccines used in Brazil are effective to achieve protection from SARS-Cov-2 even for people who have previously had the disease, according to a study published this week in The Lancet by scientists from the Vigivac project at the Oswaldo Cruz Foundation (Fiocruz).
The report states that vaccination reduces the occurrence of hospitalizations and deaths.
The researchers found that the effectiveness of immunizers against hospitalization or death, 14 or more days after completion of the vaccination schedule, was 81.3% for CoronaVac, 89.9% for AstraZeneca, and 57.7% for Janssen, and 89.7% for Pfizer.
Regarding symptomatic cases which did not require hospitalization, an effectiveness of 39.4% was found for Coronavac, 56% for AstraZeneca, 44% for Janssen, and 64.8% for Pfizer.
Many countries recommend that one dose is sufficient for previously infected individuals. We found that a second dose of CoronaVac, AstraZeneca, and Pfizer ensured significant additional protection against symptomatic infections and severe cases, the article points out.
It adds that there is a drop in antibodies in the nine months following patients' recovery and that repeated exposure to the antigen, through vaccination, can increase antibody diversity and protection against variants.
Taken together, these findings may help explain the additional benefits of a second dose among individuals who have been previously infected, despite the robust immune response produced by the first dose, the researchers went on.
The scientists identified about 213,000 symptomatic individuals who had RT-PCR testing at least 90 days after an initial coronavirus infection and also after the start of the vaccination program. Within this universe, 30,910 people were found to have confirmed cases of SARS-CoV-2 reinfection.
The analysis was based on national COVID-19 notification, hospitalization, and vaccination data from February 24, 2020, to November 11, 2021, prior to the arrival of the Omicron variant in Brazil.
The article ponders that the methodology used has limitations, such as the impossibility of comparing effectiveness according to age group, since the average age of the people analyzed was 36 years, with 75% of the public under the age of 45.
Another point raised is that the vaccines were introduced in the calendar at different times, which may cause the effectiveness of those applied earlier to be impaired in comparison with those that were applied later on since immunity tends to drop over time.
The researchers also did not have data on which variant had caused each case, which could also affect the effectiveness, and they also ponder that there may be differences in the accuracy of the RT-PCR tests used in different parts of the country.
The study was funded by Fiocruz, the National Council for Scientific and Technological Development (CNPq), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (Faperj), and the company JBS. The work was also supported by the Carlos III Health Institute, the Ministry of Science and Innovation of Spain, and the Government of Catalonia.
(Source: Agencia Brasil)