Nationwide epidemiological survey points to decelerating transmission of COVID-19 in most of Brazil

In the fourth phase of EPICOVID-19 BR, the proportion of the population with antibodies against the novel coronavirus fell from 3.8% in June to 1.4% in August in 133 cities. According to the authors, the methodology accurately estimates contagion rates in the previous 45 days.

By Karina Toledo  |  Agência FAPESP – The proportion of Brazil’s population with antibodies against the novel coronavirus fell from 3.8% in June to 1.4% in August, according to data published on September 25 for the latest phase of EPICOVID-19 BR, the largest survey of the prevalence of infection by SARS-CoV-2 conducted in Brazil. The researchers say the result is a strong sign that the epidemic is decelerating in most of the country.

The fourth phase of data collection for the project included 33,250 participants in 133 cities and was conducted on August 27-30 by a team coordinated by Pedro Hallal, Rector of the Federal University of Pelotas (UFPel), with funding from Todos Pela Saúde, an initiative led by private bank Itaú Unibanco.

The first three phases, completed in May (phase one) and June (phases two and three), covered the same cities and were supported by the Health Ministry. The results showed seroprevalence rising steadily, from 1.9% in phase one to 3.1% and 3.8% in phases two and three respectively. The exception was the North Region, where in some localities severely affected at the start of the pandemic the proportion of seropositives fell in the third phase compared with the second. 

According to Hallal, when the researchers embarked on the survey they believed SARS-CoV-2 antibodies remained in the organism for a long time, as was the case with antibodies against the similar coronavirus that caused the 2002-04 outbreak of severe acute respiratory syndrome (SARS-CoV), but recent evidence suggests the finger-prick rapid test is sensitive enough only to capture infections that are up to 45 days old, although it can also detect slightly older infections if severe.

“Initially we thought of EPICOVID-19 BR as a kind of movie that would show the evolution of seroprevalence across the country while the epidemic lasted, in a cumulative manner. Now we know the duration of antibodies is limited and all we have is a series of snapshots taken at different moments,” Hallal said. “Although it’s not possible to estimate the number of Brazilians who have come into contact with the virus at some time in their lives, we can see quite precisely the percentage who have been infected recently, and this proportion is clearly trending down.”

EPICOVID-19 BR is designed to have six phases and to estimate the percentage of Brazilians infected by the virus by age, gender, income level, place of residence, and region, as well as the proportion who are asymptomatic, and the symptoms and lethality of the disease. Its designers aim to provide input for decision making on social isolation and other public policy measures.

The other two phases will be conducted in the months ahead, thanks to support from FAPESP. Marcelo Burattini, a professor at the Federal University of São Paulo’s Medical School (EPM-UNIFESP), will be the principal investigator for these phases. Burattini was a member of the steering committee for the first four phases of EPICOVID-19 BR. 

Trends

According to Hallal, the latest results point to a change in the predominant age group among those infected in August compared with June. In the first few months of the pandemic, the level of seroprevalence was highest in the 20-50 age group, which is the most productive and also tends to disregard social isolation measures. Now the percentage has fallen in this group and risen among children and the elderly. In terms of socio-economic status (basically household income), the trend has remained stable in all phases of the survey, with the poorest 20% displaying twice the level of seroprevalence observed among the richest 20%.

Seroprevalence fell significantly in indigenous communities in recent months, as the epidemic decelerated in the North region. On the other hand, the probability of infection remains higher among people of color than among white people.

“Interiorization of the pandemic was very clear in this fourth phase,” Hallal said. “The contagion rate is now much higher in the smaller cities of the interior than in the state capitals on the coast, in stark contrast with the previous phases.”

The cities with the highest levels of seroprevalence in the latest phase were Juazeiro do Norte (8%) and Sobral (7.2%) in the state of Ceará, followed by Santarém (6.4%) and Altamira (5.2%) in the state of Pará. The highest in the state of São Paulo was Ribeirão Preto (2.8%), followed by Araçatuba (2%), Campinas (0.8%), and São Paulo City (0.8%).

“This kind of result is important as a guide to policymakers because it reveals the reality of public health conditions in each region,” Hallal said. “We regret the two-month gap in data collection due to suspension of funding from the Health Ministry. If we had been able to collect data in July and early August, we would probably have detected trends that have unfortunately been missed. Our history will tell the beginning and end of the epidemic but part of the middle has been lost. FAPESP and Todos Pela Saúde saved the survey, which offers Brazilian society a wealth of useful information.”