As the COVID-19 pandemic continues, the authorization of vaccines for emergency use has been crucial in slowing down the rate of infection and transmission of the SARS-CoV-2 virus that causes COVID-19. In order to investigate the longitudinal serological responses to SARS-CoV-2 natural infection and vaccination, a large-scale, multi-year serosurveillance program entitled SPARTA (SARS SeroPrevalence and Respiratory Tract Assessment) was initiated at 4 locations in the U.S. The serological assay presented here measuring IgG binding to the SARS-CoV-2 receptor binding domain (RBD) detected antibodies elicited by SARS-CoV-2 infection or vaccination with a 95.5% sensitivity and a 95.9% specificity. We used this assay to screen more than 3100 participants and selected 20 previously infected pre-immune and 32 immunologically naïve participants to analyze their antibody binding to RBD and viral neutralization (VN) responses following vaccination with two doses of either the Pfizer-BioNTech BNT162b2 or the Moderna mRNA-1273 vaccine. Vaccination not only elicited a more robust immune reaction than natural infection, but the level of neutralizing and anti-RBD antibody binding after vaccination is also significantly higher in pre-immune participants compared to immunologically naïve participants (p<0.0033). Furthermore, the administration of the second vaccination did not further increase the neutralizing or binding antibody levels in pre-immune participants (p=0.69). However, ~46% of the immunologically naïve participants required both vaccinations to seroconvert.

Determining reinfection rates and correlates of protection against SARS-CoV-2 infection induced by both natural infection and vaccination is of high significance for the prevention and control of coronavirus disease 2019 (COVID-19). Furthermore, understanding reinfections or infection after vaccination and the role immune escape plays in these scenarios will inform the need for updates of the current SARS-CoV-2 vaccines and help update guidelines suitable for the postpandemic world.

In order to longitudinally track SARS-CoV-2 antibody levels after vaccination or infection, we assessed anti-RBD antibody levels in over 1000 people and found no significant decrease in antibody levels during the first 14 months after infection in unvaccinated participants, however, a significant waning of antibody levels was observed following vaccination. Participants who were pre-immune to SARS-CoV-2 prior to vaccination seroconverted to higher antibody levels, which were maintained at higher levels than in previously infected, unvaccinated participants. Older participants exhibited lower level of antibodies after vaccination, but a higher level after infection than younger people. The rate of antibody waning was not affected by pre-immunity or age. Participants who received a third dose of an mRNA vaccine not only increased their antibody levels ~14-fold, but also had ~3 times more antibodies compared to when they received their primary vaccine series. PBMC-derived memory B cells from 13 participants who lost all circulating antibodies were differentiated into antibody secreting cells (ASCs). There was a significant recall of memory B cell ASCs in the absence of serum antibodies in 5–8 of the 10 vaccinated participants, but not in any of the 3 infected participants, suggesting a strong connection between antibody levels and the effectiveness of memory B cell recall.

Introduction: Universities are unique settings with large populations, congregate housing, and frequent attendance of events in large groups. However, the current prevalence of previous COVID-19 infection in university students, including symptomatic and asymptomatic disease, is unknown. Our goal therefore was to determine the prevalence of previous infection, risk factors for infection, and the prevalence of persistent symptoms following infection among university students.Methods: This was a cross-sectional study set in a large public university between January 22 and March 22, 2021. We surveyed students about demographics, risk factors, and symptoms, and simultaneously tested their saliva for IgA antibodies to SARS-CoV-2. To estimate the prevalence of previous infection we adjusted our intentional sample of a diverse student population for year in school and age to resemble the composition of the entire student body and adjusted for the imperfect sensitivity and specificity of the antibody test. Univariate and multiple regression analysis was used to identify independent risk factors for infection, and the proportion of students with persistent symptoms following acute infection was determined.Results: A total of 488 students completed the survey, 432 had a valid antibody result, and 428 had both. The estimated prevalence of previous infection for 432 participants with valid antibody results was 41%. Of 145 students in our sample with a positive antibody test, 41.4% denied having a previous positive polymerase chain reaction (PCR) test for SARS-CoV-2 and presumably had an asymptomatic infection; in our adjusted analysis we estimate that approximately 2-thirds of students had asymptomatic infections. Independent risk factors for infection included male sex, having a roommate with a known symptomatic infection, and having two or fewer roommates. More frequent attendance of parties and bars was a univariate risk factor, but not in the multiple regression analysis. Of 122 students reporting a previous symptomatic infection, 14 (11.4%) reported persistent symptoms consistent with postacute COVID-19 a median of 132 days later.Conclusions and Relevance: Previous COVID-19 infection, both symptomatic and asymptomatic, was common at a large university. Measures that could prevent resurgence of the infection when students return to campus include mandatory vaccination policies, mass surveillance testing, and testing of sewage for antigen to SARS-CoV-2.