SARS-CoV-2 seroconversion in response to infection and vaccination: A time series local study in Brazil

The investigation of antibodies raised against different SARS-CoV-2 antigens can help to determine the extent of previous SARS-CoV-2 infections in the population and track the humoral response to vaccination. Therefore, serological surveys can provide key information to better manage the pandemic and/or to implement the most effective vaccination program. Here we describe a time series anti-Nucleocapsid, anti-Spike IgG serological survey analysis in the city of Matinhos, PR, Brazil during the year of 2021. Seroconversion rates to the Nucleocapsid antigen was not influenced by gender or age. Comparison of the serological data with official COVID-19 cases in the city suggest that case sub notification is higher than 47%. Furthermore, by applying serological data, the corrected infection fatality rate was estimated to be lower than 2.4 % in contrast with the official estimative of 3.6 %. The rates of IgG reactive to Spike antigen resembled the curve of the fraction the population that had taken the second vaccine dose. Up to 82% of Spike seroconversion was detected in the end of 2021 confirming the effective of the COVID-19 vaccination program in the city. This SARS-CoV-2 serological study unraveled the SARS-CoV-2 infection rates and the response to vaccination in the city of Matinhos. It is likely that the numbers reported here may be similar in other cities in Brazil.