Nationwide survey shows that several COVID-19 epidemics are under way in Brazil

Supported by FAPESP and led by a researcher at the Federal University of São Paulo, EPICOVID-19 BR 2 tested 120,000 people in 133 cities between January 25 and April 24, 2021. Amazonas was the state with the highest seroprevalence, with positive test results accounting for 31.4%. The nationwide average was 15%.

Agência FAPESP – In the first year of the COVID-19 pandemic in Brazil, the novel coronavirus spread to all regions of the country. By the end of April 2021, with the contagion curve on the rise, 15% of Brazilians tested as part of the EPICOVID-19 BR 2 survey had antibodies against SARS-CoV-2.

Seroprevalence rates varied widely, however, from 9.89% in Ceará to 31.4% in Amazonas, the state with the highest seroprevalence in Brazil. The survey, supported by FAPESP and coordinated by Marcelo Burattini, a professor at the Federal University of São Paulo (UNIFESP), tested 120,000 people in 133 cities throughout Brazil between January 25 and April 24, 2021.

“The vast majority of the people in the sample hadn’t been vaccinated, as most of the testing was done in January and the first half of February, when the national vaccination program was only just beginning,” Burattini said. “Fewer than 1% of the people tested said they had been vaccinated, and practically none had received both doses.” The survey, therefore, made no distinction between interviewees who had or had not been vaccinated.

The survey also highlighted significant variations between regions in terms of seropositivity. In the Southeast, for example, antibodies against the virus were detected in 19.57% of the samples from Rio de Janeiro state, 18.73% in Espírito Santo state and 13% in São Paulo state.

There were also variations within states. In São Paulo state, seroprevalence averaged 9% in Sorocaba and Bauru, 20% in Marília, and 13%-15% in São José do Rio Preto, Araçatuba, Ribeirão Preto and São José dos Campos.

“These results point to considerable spatial variation in the epidemic. In fact, there are several epidemics in Brazil, rather than just one. Variations exist across the entire country, and will be one of the objects of more detailed study in this project,” Burattini said.

In Araraquara (São Paulo state), for example, 258 people were tested in the period, and seroprevalence was only 4%. A short while later, between January 21 and March 2, the city declared lockdown to contain an explosion of cases and reduce overcrowding of intensive care units (ICUs).

“The survey sample yield was very low. This could explain the later explosion of cases, but we can’t be absolutely sure,” Burattini said.

The preliminary results of the survey, he added, suggest seroprevalence was significantly lower than it should be if the predictions published until then on the proportion of asymptomatic cases had been accurate. “Once we’ve completed our analysis of all 133 cities and compared the data from the survey with the notified occurrences of COVID-19, we’ll have important information for use by policymakers. This will probably lead to a new understanding of the dynamics of the disease and its occurrence in our community,” he said.

EPICOVID-19 BR 2 was designed to estimate the percentage of Brazilians infected by SARS-CoV-2 by age, gender, income level, place of residence and region, determine the proportion who are asymptomatic, and survey the symptoms and lethality of the disease. Its designers aim to provide input for policymaking and evaluate the impact of social distancing, lockdowns and other measures taken to control the epidemic, such as mask-wearing.

The other variables surveyed apart from seroprevalence are still being analyzed, given the number of people in the sample, Burattini said.

Complementary studies

EPICOVID-19 BR 2 complements EPICOVID-19 BR, a four-phase survey led by Pedro Hallal of the Graduate Program in Epidemiology at the Federal University of Pelotas (UFPEL). The first three phases were funded by the Ministry of Health and the fourth by Todos Pela Saúde, an initiative led by Itaú Unibanco, Brazil’s largest private bank.

Seroprevalence averaged 2.9% nationwide in the first phase (May 14-21, 2020) and 4.6% in the second (June 4-7). This latter percentage was repeated in the third phase (June 21-24), but fell to 1.2% in the fourth (August 27-30).

“The discrepancy between Phase 4 and the rest is being investigated,” said Burattini, who also participated in the first survey.

“EPICOVID-19 BR 2 is an independent survey, which is related to the previous one in that it uses the same geographic basis and a similar sampling methodology,” he said.

Data collection in the four phases of the UFPEL survey took place in 133 cities and 25 census sectors, drawing lots to select ten households per sector and one resident per household, for a total of 33,250 participants in each phase.

“In all phases, antibodies against SARS-CoV-2 were detected by the lateral flow rapid serology test using a finger prick sample,” Burattini explained.

EPICOVID-19 BR 2, led by Burattini, covered the same cities and census sectors but selected eight households per sector owing to budget constraints, aiming to test 1,000 people per city. 

“Differently from the four phases of the first survey, all members of the households selected by lot took part in the second survey, multiplying the number of people tested from about 33,000 to over 120,000,” he said.

Another key difference was that in the latest phase the rapid test was replaced by venipuncture to collect blood samples for serological analysis to detect total antibodies by electrochemiluminescence immunoassay (ECLIA). “The next steps include a complete analysis of the material obtained and publication of the results, which should happen in the course of the coming months,” Burattini said.