Population-level seropositivity trend for SARS-Cov-2 in Rio Grande do Sul, Brazil

Abstract

OBJECTIVE: To describe the evolution of seropositivity in the State of Rio Grande do Sul, Brazil, through 10 consecutive surveys conducted between April 2020 and April 2021. METHODS: Nine cities covering all regions of the State were studied, 500 households in each city. One resident in each household was randomly selected for testing. In survey rounds 1–8 we used the rapid WONDFO SARS-CoV-2 Antibody Test (Wondfo Biotech Co., Guangzhou, China). In rounds 9–10, we used a direct ELISA test that identifies IgG to the viral S protein (S-UFRJ). In terms of social distancing, individuals were asked three questions, from which we generated an exposure score using principal components analysis. RESULTS: Antibody prevalence in early April 2020 was 0.07%, increasing to 10.0% in February 2021, and to 18.2% in April 2021. In round 10, self-reported whites showed the lowest seroprevalence (17.3%), while indigenous individuals presented the highest (44.4%). Seropositivity increased by 40% when comparing the most with the least exposed. CONCLUSIONS: The proportion of the population already infected by SARS-Cov-2 in the state is still far from any perspective of herd immunity and the infection affects population groups in very different levels.

Seroepidemiology of SARS-CoV-2 on a partially vaccinated island in Brazil: Determinants of infection and vaccine response

“…Compared to surveys conducted in Brazil around mid-2021 the seroprevalence of antibodies against SARS-CoV-2 in our sample (53.61%) was higher than other studies reported in the South and Southeast regions of Brazil ( 14 , 16 , 17 ), being closer to rates observed at that time in the North region ( 18 , 19 ) and in indigenous populations ( 20 , 21 ). With a vaccine coverage of 37% in our study population, the large difference in seroprevalence between vaccinated (90.5%) and unvaccinated (31%) residents confirmed findings from other studies ( 22 ) of how vaccination decisively contributes to the population's immunity, even in an area with a high prevalence of infection-induced antibodies after exposure to a pandemic for more than a year.…”

From a recombinant key antigen to an accurate, affordable serological test: Lessons learnt from COVID-19 for future pandemics

“…Furthermore, tests that present high accuracy allow deeper epidemiological analyses to be made. For example, in a population-based COVID-19 epidemiological study (EPICOVID-RS) carried out in 9 different cities in Rio Grande do Sul state (Brazil), the high accuracy of the S-UFRJ test (used from the 9 th study round on) allowed the determination of a logit-linear relationship between the exposure level of study participants and the seroprevalence [6] . In the 8 first rounds of the study, a commercial rapid antibody test had been used, but it was replaced by the S-UFRJ test after a comparative evaluation indicated a clear superiority of the S-UFRJ ELISA [33] .…”

Structural factors associated with SARS-CoV-2 infection risk in an urban slum setting in Salvador, Brazil: A cross-sectional survey

“…In this community-based study conducted in the city of Salvador, Brazil, we found that nearly half of residents in an urban slum had evidence of SARS-CoV-2 infection after the first wave of the epidemic in 2020 and before the peak of the second wave. In contrast, cross-sectional surveys conducted among blood donors in the states of São Paulo and Rio Grande do Sul estimated 10% to 30% seroprevalence in February 2021, when our data collection ended [ 25 , 26 ]. This finding is consistent with studies in other settings that reported higher seroprevalence in slums than in non-slum settings [ 4 , 27 ], highlighting the increased vulnerability of socioeconomically deprived communities.…”