ABSTRACT
The durability of the antibody response following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections has not been fully elucidated. We have performed a cross-sectional study in one of the largest slums of Buenos Aires, Barrio Padre Mugica in June 2020, detecting a seroprevalence of 53.4%. To evaluate the persistence of the humoral response against SARS-CoV-2 in this area, we designed a second study assessing only the people that were IgG positive in the first survey. The IgG levels against the full spike (S) protein in 175 individuals that were seropositive, at least 6 months before, were evaluated in a second survey. The positivity rate was 92.0%, 161 from 175 individuals remained IgG positive. We observed a contraction in the overall IgG levels measured by ELISA. The median IgG dropped 62% from June to December 2020. Most of the individuals tested (87%) reported to be asymptomatic or oligo-symptomatic. No difference was found between men and women, but people aged less than 50 showed a lower IgG level in each period compared to older individuals. Our data indicate sustained humoral immunity for at least 6 months in a specific socio-economical setting in a population that was mainly asymptomatic for COVID-19.
ABSTRACT
BackgroundBy July 1st, the incidence rate of RT-qPCR SARS-CoV-2 infection was 5.9% in Barrio Padre Mugica, one of the largest slums in Buenos Aires City. This study aimed to establish the seroprevalence of SARS-CoV-2 three months after the first case was reported. MethodsBetween June 10th and July 1st, a cross-sectional design was carried out on people over 14 years old, selected from a probabilistic sample of households. A finger prick sample was tested by ELISA to detect IgG-class antibodies against SARS-CoV-2. Multilevel model was applied to understand sector, household and individual conditions associated with seroconvert. ResultsPrevalence based on IgG was 53.4% (95%IC 52.8% to 54.1%). Among the IgG positive cases, 15% reported having compatible symptoms at some point in the past two months. There is evidence of within-household clustering effect (rho=0.52; 95% IC 0.36-0.67); living with a PCR-confirmed case doubled the chance of being SARS-CoV2 IgG positive (OR 2.13; 95% IC 1.17-3.85). The highest risk of infection was found in one of the most deprived areas of the slum, the "Bajo autopista" sector. DiscussionHigh seroprevalence is shown, for each symptomatic RT-qPCR-confirmed diagnosis, 9 people were IgG positive, indicating a high rate of undetected (probable asymptomatic) infections. Given that transmission among family members is a leading driver of the diseases spread, it is unsurprising that crowded housing situations in slums are directly associated with higher risk of infection and consequently high seroprevalence levels. This study contributes to the understanding of population immunity against SARS-CoV2, its relation to living conditions and viral spread, for future decision making.
