Remarkable Variability in SARS-CoV-2 Antibodies across Brazilian Regions: Report on Two Successive Nationwide Serological Household Surveys

Background: Population based data on COVID-19 are essential for guiding public policies. There are few such studies, particularly from low or middle-income countries. Brazil is currently a hotspot for COVID-19 globally. Methods: We report on two waves of seroprevalence surveys relying upon on household probabilistic samples of 133 large sentinel cities in all Brazilian states, including 25,025 participants in the first wave (May 14-21) and 31,165 in the second wave (June 4-7). Presence of antibodies against SARS-CoV-2 was assessed using a lateral flow point-of-care test. Seroprevalence estimates were adjusted for test’s sensitivity and specificity. Results: For the 83 cities with sample sizes of 200 or more tests in both phases, the pooled seroprevalence increased from 1.9% (95% CI 1.7%;2.1%) to 3.1% (2.8%;3.4%) over the 3-week period. City-level prevalence ranged from 0.0% to 25.4% in both phases. Eleven of the 16 cities with prevalence above 2.0% in the first wave were located in a stretch along the Amazon river in the Northern region; in the second wave, there were 34 cities with prevalence above 2%, which included the same 11 Amazon cities as well as 14 from the Northeast region, where prevalence is increasing rapidly. Prevalence levels were markedly lower in the South and Centre-West regions, and intermediate in the Southeast, where the highest level was found in Rio de Janeiro at 7.5% (4.2%;12.2%) in the second wave. In the second round, prevalence was similar in men and women, but higher levels were observed for subjects aged 20-59 years, and for those living in crowded conditions. Indigenous people had prevalence levels 6.4% (4.1%;9,4%) compared to 1.4% (1.2%;1.7%) among whites. Prevalence in the poorest socioeconomic quintile was 3.7% (3.2%;4.3%) compared to 1.7% (1.4%;2.2%) in the wealthiest quintile. Interpretation: Our results suggest that pandemic is highly heterogenous, with rapid escalation in Brazil’s North and Northeast, and slow progression in the South and Center-West regions. Prevalence is strongly associated with indigenous ancestry and low socioeconomic position.