The first shot protects, but immunization requires a second dose and varies according to group and to the time interval between the doses. These are some conclusions of the pre-publication study that evaluated the effectiveness of the first dose of the AstraZeneca/Fiocruz vaccine against symptomatic cases of Covid-19 in the population of Complexo da Maré, in Rio de Janeiro (RJ). A 42.4% protection against symptomatic cases was estimated 21 days after the first dose of the vaccine. “It has a good result for containing symptomatic cases, but the second dose is essential to guarantee more complete immunity and broader protection for the community”, guarantees Fernando Bozza, coordinator of the study and researcher at Fiocruz.
The 42.4% effectiveness is in line with previous evaluations of the effectiveness of the first dose of AstraZeneca/Fiocruz in the context of the Gamma or Delta variant. It was also found that younger people had greater protection than older people. While in the population below 35 years the effectiveness was 57.5%, in the population above 35 years it was 34.8%. Another fact is that protection increases over time, from 40 days onwards. Effectiveness reaches 58.9%, considering all age groups above 18 years between days 42 and 55 after the first dose, and starts to drop after that.
Evaluating the impact of the pandemic specifically on vulnerable communities was also one of the objectives. More general data tend to neglect this particularity and homogenize contexts, which makes it difficult to adopt more effective policies for each reality. The study highlights that other analysis have confirmed Covid-19 disproportionate impact on this type of community. “This is due to persistent social, economic and health inequalities”, highlights Fernando Bozza. “Although the effectiveness of vaccines has already been verified in high-income countries, there is a lack of papers estimating its effectiveness in contexts of greater vulnerability”, he explains.
The method employed by the study was the so-called negative test design (NTD), which compares patients who tested positive for Covid-19 with patients who did not test positive. The period covered, between January 17 and September 14, was characterized by a predominance of the Gamma and Delta variants.
Innovation in community involvement
The experience at Maré would be an exemplary case for the innovation in involving the community in the mobilization process for vaccination and for the study of its effectiveness. “This is the first study that estimates the vaccine's protection for the population of a neglected community that was heavily affected by the pandemic,” says Bozza. "When it comes to studies, there is a tendency to focus on numbers, results, but in this case, the entire process of working with primary care and mobilizing the population is very important.” For him, the involvement of the community in the research changed the perspective on the work and ensured more consistent results.
