The percentage of Brazilians with antibodies against the new coronavirus fell from 3.8% in June to 1.4% in August, according to the results of the fourth phase of the Epicovid-19 BR survey, released last week. For the authors, the data show that the epidemic is decelerating in most of the country.
Epicovid-19 BR is the largest Covid-19 prevalence survey underway in the country. Data from the most recent phase were collected between August 20 and 23, with the participation of 33,250 people from 133 Brazilian cities. As in the other stages, interviewers visited homes and did quick interviews and tests (with a drop of blood taken from the finger) of antibodies to Sars-CoV-2, the virus that causes Covid-19.
At the beginning of the pandemic, experts believed that antibodies produced after a new coronavirus infection would remain in the human body for a long time, but research has shown that this is not the case. Studies in several countries have shown that antibodies can disappear from the blood of people recovered from the disease in two or three months – but that does not mean that they are not immune to a new infection, since antibodies are only part of the defense against virus.
“Initially, we treated Epicovid as a video camera, which could show the evolution of seroprevalence in the country throughout the epidemic, cumulatively. Now we know that antibodies have a limited duration and, therefore, what we have are several photographs from different moments. Although it is not possible to estimate the total number of Brazilians who have had contact with the virus at some point in their lives, we can accurately see the percentage of people who have recently been infected and this number is clearly falling “, explains Pedro Hallal, research coordinator, to Fapesp Agency.
In the previous three stages – one completed in May and the other two in June, in the same 133 cities – seroprevalence had followed an upward trend: 1.9%, 3.1% and 3.8%, respectively. The exception was the North region, where some regions that were strongly affected in the beginning of the pandemic registered a drop in the percentage of people with antibodies in the second and third phases of the study. Two other stages of the research are yet to be carried out.
Hallal told Agência Fapesp that the results of the fourth phase clearly show the interiorization of the pandemic. “Today the virus is much stronger in cities in the interior than in capitals – which is very different from what was observed in the previous phases”, he commented.
The researcher pointed out that in the first months of the pandemic, seroprevalence was greater among people aged 20 to 50 – those of working age and who had more difficulty maintaining social isolation. At this stage, the proportion decreased in this group and increased among children and the elderly.
People from families that are among the poorest 20% of the population have a prevalence more than twice as high as that observed among the richest 20%. This trend did not change between the phases of the study.
There was a decrease in the prevalence of antibodies among the indigenous population, explained by the slowdown in the epidemic in the North. Blacks and browns continue to have a higher chance of infection compared to whites.
The cities with the highest seroprevalence in the most recent measurement were Ceará, Juazeiro do Norte (8%) and Sobral (7.2%), followed by Santarem (6.4%) and Altamira (5.2%). In the state of São Paulo, the first places are Ribeirão Preto (2.8%), Araçatuba (2%), Campinas (0.8%) and the capital (0.8%).