Prevalence and predictors of anti-SARS-CoV-2 serology in a highly vulnerable population of Rio de Janeiro: A population-based serosurvey

Abstract

Background: COVID-19 serosurveys allow for the monitoring of the level of SARS-CoV-2 transmission and support data-driven decisions. We estimated the seroprevalence of anti-SARS-CoV-2 antibodies in a large favela complex in Rio de Janeiro, Brazil.

Methods: A population-based panel study was conducted in Complexo de Manguinhos (16 favelas) with a probabilistic sampling of participants aged ≥1 year who were randomly selected from a census of individuals registered in primary health care clinics that serve the area. Participants answered a structured interview and provided blood samples for serology. Multilevel regression models (with random intercepts to account for participants' favela of residence) were used to assess factors associated with having anti-S IgG antibodies. Secondary analyses estimated seroprevalence using an additional anti-N IgG assay.

Findings: 4,033 participants were included (from Sep/2020 to Feb/2021, 22 epidemic weeks), the median age was 39·8 years (IQR:21·8-57·7), 61% were female, 41% were mixed-race (Pardo) and 23% Black. Overall prevalence was 49·0% (95%CI:46·8%-51·2%) which varied across favelas (from 68·3% to 31·4%). Lower prevalence estimates were found when using the anti-N IgG assay. Odds of having anti-S IgG antibodies were highest for young adults, and those reporting larger household size, poor adherence to social distancing and use of public transportation.

Interpretation: We found a significantly higher prevalence of anti-S IgG antibodies than initially anticipated. Disparities in estimates obtained using different serological assays highlight the need for cautious interpretation of serosurveys estimates given the heterogeneity of exposure in communities, loss of immunological biomarkers, serological antigen target, and variant-specific test affinity.

Funding: Fundação Oswaldo Cruz, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ), the European Union's Horizon 2020 research and innovation programme, Royal Society, Serrapilheira Institute, and FAPESP.

Keywords: Antibodies; Brazil; COVID-19; Serosurveys; Social inequity.

Figure 1

Prevalence of reactive anti-SARS-CoV2 serology (anti-S IgG) by favela.

Figure 2

Space and time dynamics of anti-SARS-CoV 2 prevalence (anti-S IgG antibodies) in Manguinhos.

Figure 3

Prevalence of Anti-S IgG antibodies and median titers of serologic results among study participants over the study period. Anti-S IgG antibodies titers are median values of reactive results each week. Prevalence of SARS-CoV-2 Zeta (P2) and Gamma (P1) variants in Rio de Janeiro state over the study period, source: Corona-ômica-RJ Network (http://www.corona-omica.rj.lncc.br/).

Figure 4

Predicted probabilities of reactive Anti-SARS-CoV 2 serology (Anti-S IgG) as estimated from adjusted logistic multilevel regression models.

Figure 5

Prevalence estimates of Anti-N IgG carriers and Anti-S IgG carriers by age.

Figure 6

Quantitative Anti-S IgG antibodies level among individuals with reactive serology by age strata. Violin plot and box plot showing the density distribution, median, first and third quartiles of Anti-S IgG antibodies titers by age strata.