Long-term COVID-19 Immune Response in a Vulnerable Neighbourhood in Argentina

Background Between June 10t h and July 1st, a cross-sectional design study was carried out in an Argentina slum over people, selected from a probabilistic sample of households showed a prevalence based on IgG-class antibodies against SARS-CoV-2 of 53.4%. In regarding to the persistence of these antibodies, the early data brought hope that acquired immunity was possible. But some subsequent studies have suggested that immune protection might be short-lived. The new findings show that people who survive a COVID-19 infection continue to produce protective antibodies against key parts of the virus for at least three to four months after developing their first symptoms. In contrast, some other antibody types decline more quickly.

It remains unanswered whether natural infection produces a sustained immunity that is capable of establishing herd immunity. The other health problem that Latin America faces is dengue, whose transmission, like SARS-CoV-2, is greater in areas with high population density such as vulnerable neighborhoods. In this context, the occurrence of the two diseases implies a risk, particularly in regions with several dengue serotypes where secondary and tertiary infections have been demonstrated and dengue epidemiological surveillance has been affected by the saturation of health system.

Objectives The aim of this study is to evaluate the presence of IgG antibodies for COVID-19 after 5 months in inhabitants of this slum who consented the Seroprevalence Study for COVID-19, and to evaluate those factors associated with the persistence of positive antibodies. As a secondary objective, the presence of positive IgG for dengue will be evaluated.

Methods Cross sectional study. Population of the study were inhabitants of the slum: men and women form 14 years of age or older were included. People will be invited to participated and detection of antibodies will be performed with ta serological tests, an enzyme linked immunosorbent assay (ELISA) developed and validated in Argentina which detects antibodies against two viral antigens, trimeric spike and the receptor binding domain (RBD) of the spike protein. Blood sample will be collected in a capillary tube from a finger prick taken at the doorstep of each person. Samples will be processed and analyzed at the "Hospital de Niños Doctor Ricardo Gutierrez" Virology laboratory.

Blood sample collection and epidemiological data were collected, and entered in a secure database.

Sample Size The first seroprevalence study included 426 inhabitants of 14 years or more. Considering a persistence of antibodies of 30% with a precision of 5% for a confidence interval of 95% 184 inhabitants should be included. This sample will be selected by a proportionate stratified random sampling, considering the ten sectors in which the slum is divided.

Statistical analysis Descriptive statistics of the data will be carried out according to the variables obtained. Continuous variables will be expressed as mean and standard deviation, and categorical variables as proportions. A multiple logistic regression model will be performed to evaluate the factors associated with the persistence of positive antibodies for SARS-CoV-2.

Dengue seroprevalence is determined globally and by geographic sector. R software version 4.0.2 will be used.