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Study in a favela in Rio de Janeiro proves the effectiveness of the COVID-19 vaccine


Hellen Guimarães (Fiocruz News Agency)


Vaccination can protect the population against contamination, hospitalization, and death by COVID-19, even in socially vulnerable communities with high transmission rates. This is one of the main conclusions of a new paper of the "Vacina Maré" (vaccinate Maré, in english) research, which evaluates the effectiveness of the Fiocruz/AstraZeneca vaccine against getting sick with COVID-19, in Complexo da Maré, a complex of favelas in the North Zone of Rio de Janeiro. The research was recently published on the magazine "Clinical Microbiology and Infection", of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID). The paper analyzed the gradual increase in protection after vaccination and confirmed that three weeks after the first dose, protection against symptomatic COVID-19 is of 31.6%. Two weeks after the second dose, this rate reaches 65.1%.

Mass vaccination reduced mortality among the favela population

The results obtained after the second dose confirm the conclusions found in the previous version of the paper, made public in November, which dealt with the data referring to vaccination of Maré inhabitants with the first dose. The evidence further reinforces the importance of the second dose to ensure a more robust and prolonged response, since the effects of the first dose begin to wane after a few months. 

“How effective is the vaccine in terms of protecting people and preventing them from being infected by the virus? Are vaccinated people protected from infection by the virus? This is the great question posed by the paper, and the answer is yes. Today many people say the vaccine does not protect against the disease, only against hospitalization and death. This is not true. Of course, protection against severe forms of the disease is higher. Vaccinated people can be infected and remain asymptomatic or have milder symptoms. On the other hand, plenty of people will not get the disease because they are vaccinated”, explained Fernando Bozza, Fiocruz researcher and coordinator of the study.
The research is carried on by Fiocruz in partnership with the Department of Industrial Engineering of PUC-Rio, the Global Health Institute of Barcelona, and the Local Government of Rio de Janeiro, by means of its Local Government Health Secretary’s Office. It relies on the support of Redes da Maré and Projeto Conexão Saúde – De Olho na COVID and is financed by the Bill and Melinda Gates Foundation. The verified data reinforce the importance of vaccination as a core defense against the pandemic.

“The vaccine provides protection at all levels: it protects against death, hospitalization, and against acquiring the virus or getting sick from it. Of course, these levels are different: here we are talking about 65% against getting the virus after the second shot. This reaches more than 80% or 90% when it comes to protection against hospitalization and death”, he stated. According to the data made available by the Rio Covid Panel, of the Local Government, between October 30 of the past year and January 18 of the present year, when it was last updated, there were no COVID-19 deaths at Maré community.


Researchers crossed information from the database of the Fiocruz testing program and that of the vaccination program. The method used was the negative test study (NTS, in portuguese)), dividing those who contracted the virus in two groups: one with symptomatic individuals and another with all those infected (with or without symptoms). The analysis encompassed 10.077 RT-PCR tests, of which 6.394 (64%) were symptomatic and 3.683 (36%) had no symptoms. The reference period, between January 17 and November 27, 2021, was characterized by a mixed predominance of the Gamma and Delta variants. The study, which is still ongoing, intends to evaluate, during its next phase, the effectiveness of the vaccine against the Ômicron variant and regarding the booster shot.

The study took these four aspects into account: the first related to the pandemic time; the second, a complete adjustment (which considers variables such as gender, cardiovascular disease, respiratory disease, underlying health issues, all characteristics related to the worsening or acquisition of the disease); the third, age, separating the participants into a group of people below 35 and another 35 and up; and finally, the fourth, which takes into account the time span between the first and the second dose.

“In general, the differences in effectiveness are very small. Adjustments are made to show that regardless of the focus of the analysis, vaccination is effective in controlling the pandemic and has direct influence on the drop in the number of cases. These do not fall by themselves just because the pandemic has been around for a while. Mass vaccination was probably crucial to prevent Delta from expanding even further. We had a peak of Gamma activity in Brazil between 2020 and 2021, and the Delta variant was introduced right after that. At Maré, this Delta peak practically did not happen, probably because vaccination had been effective and blocked these transmission chains”, he explained.

The greatest variation was observed in the age aspect. Among younger people (below 35), protection after the second shot was 89.2%. From 35 years old, vaccine effectiveness is 55.6%. “There are some factors involved, including immune response, which explain how elderly people create this vaccine immune response. Seroconversion studies show that they develop less antibodies than young people after vaccination. They have more need of the booster shot, just like immunosuppressed individuals”, he said.

Originality and the importance of research at Maré

Rio’s largest group of favelas, with about 140,000 residents, Maré is home to mass vaccination and testing initiatives carried out by an integrated action between the Local Government Health Secretary’s Office, Fiocruz, and Redes da Maré. The study of vaccine effectiveness in the region, coordinated by the Foundation, proposes a point of view that takes into account characteristics that are unique to the territory - high populational density, unique transmission chains, high levels of virus circulation, and the social vulnerability of the population.

“The state of Rio de Janeiro had the highest lethality during a good part of the pandemic, and Maré had one of the highest lethality rates, especially early in the pandemic. It was higher than that of the city and of the state, and at a certain point it was twice as high as the rate found in the city as a whole. A series of steps was taken, involving more than vaccination. Fiocruz provided support to an entire testing strategy, communication, and follow-up of people with COVID-19, and this pulled this lethality rate downward”, emphasized Bozza. 

The goal to vaccinate the entire adult population of Maré was accomplished: 93.4% of the target public was immunized with two doses of the AstraZeneca vaccine. The results are very obvious. “After vaccination, we really saw death rates plummet. Data show that we had not had any deaths by COVID-19 at Maré in a few months. This is evidence that we have achieved high protection, even considering international standards”, he completed.

Fiocruz is also developing a cohort study at Maré, following about two thousand families and eight thousand people, including children, in a long-term monitoring system to evaluate transmission within households, the dynamics of virus circulation in the communities, and indirect protection. Genomic surveillance, which sequences samples of the virus found at Maré to detect variants, is also ongoing. “We must remain active to make sure there are other variants not yet identified in circulation within the Brazilian territory and which may result in further developments regarding the pandemic”, concluded Bozza.

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