Serological survey to estimate SARS-CoV-2 infection and antibody seroprevalence at a large public university: A cross-sectional study

Abstract

Objective: This study investigated the seroprevalence of SARS-CoV-2 antibodies among adults over 18 years.

Design: Prospective cohort study.

Settings: A large public university.

Participants: This study took volunteers over 5 days and recruited 1064 adult participants.

Primary outcome measures: Seroprevalence of SARS-CoV-2-specific antibodies due to previous exposure to SARS-CoV-2 and/or vaccination.

Results: The seroprevalence of the antireceptor binding domain (RBD) antibody was 90% by a lateral flow assay and 88% by a semiquantitative chemiluminescent immunoassay. The seroprevalence for antinucleocapsid was 20%. In addition, individuals with previous natural COVID-19 infection plus vaccination had higher anti-RBD antibody levels compared with those who had vaccination only or infection only. Individuals who had a breakthrough infection had the highest anti-RBD antibody levels.

Conclusion: Accurate estimates of the cumulative incidence of SARS-CoV-2 infection can inform the development of university risk mitigation protocols such as encouraging booster shots, extending mask mandates or reverting to online classes. It could help us to have clear guidance to act at the first sign of the next surge as well, especially since there is a surge of COVID-19 subvariant infections.

Keywords: COVID-19; Epidemiology; SARS-CoV-2.

Figure 1

Comparison of assays. (A) Venn diagrams showing overlap of positive results of RBD and (B) nucleocapsid from different assays. (C) Correlation between the anti-RBD IgG by Beckman and the MSD assays. (D) Correlation between anti-NC by Bio-Rad assay and MSD assays. A red dotted line indicates the cut-off line where test values equal or greater than this line are considered positive. MSD, Meso Scale Discovery; NC, nucleocapsid; RBD, receptor binding domain.

Figure 2

Anti-RBD antibody decay postvaccination. The antibody level is determined by the Beckman semiquantitative immunoassay. The linear regression of different vaccines to estimate vaccine decay. RBD, receptor binding domain.

Figure 3

Antibody response in participants with or without previous COVID-19 infection, vaccination or both: (A) Anti-RBD antibodies measured using Beckman immunoassay in participants who had previous COVID-19 infection or COVID-19 vaccines or both. Participants were categorised by the vaccine or COVID-19 infection and time interval from vaccination/infection to blood collection. (B) Antinucleocapsid antibodies measured using MSD in participants who had previous COVID-19 infection. Participants were categorised by the COVID-19 infection and time interval from infection to blood collection. (C) Anti-RBD antibodies after breakthrough infection, hybrid immunity and vaccine only. Participants were categorised based on the order and the time of COVID-19 infection and vaccination for each group. The blue bottle indicates vaccination, the virus indicates natural infection based on participant self-reporting, and the red vial indicates blood collection. Anti-RBD IgG level is measured by Beckman immunoassay. Cut-off is defined by the manufacturer. *P- value is calculated by the Mann-Whitney U test. *p-value <0.05, **p-value <0.01, ***p-value <0.001 and ****p-value <0.0001. RBD, receptor binding domain.