The omicron variant of SARS-CoV-2 drove broadly increased seroprevalence in a public university setting

Abstract

Omicron is the comparatively most transmissible and contagious variant of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). We conducted a seroprevalence study from March 1-3, 2022, to investigate the seroprevalence of SARS-CoV-2 antibodies among individuals aged 18 years and older after the Omicron outbreak. The seroprevalence of anti-receptor binding domain (RBD) antibodies was found to be 96.3% (95% CI 95.2-97.2%) compared to 88.2% (95% CI 86.1-90%) in our previous serosurvey. For anti-nucleocapsid (NC) antibodies, the seroprevalence was 39.1% (95% CI 36.6-41.7%) compared to 19.7% (95% CI 17.5-22.2%) earlier. Individuals that experienced breakthrough infections exhibited the highest levels of anti-RBD antibodies. Additionally, saliva samples showed promise as a potential diagnostic biofluid for measuring antibody levels, as they exhibited a strong agreement with the data obtained from serum samples. The near doubling of anti-NC reactivity, a proxy for history of infection, reflects the contagiousness of the omicron variant, but may also have been influenced by a more relaxed approach to precautions in the spring of 2022. Serosurveys repeated at regular intervals monitor the trend of infections in the community, delineate the geographical spread of the infection, and may guide containment measures in communities, and prompt response to future outbreaks.

Fig 1. Flowchart of the study design.

Recruitment, sample selection, and the assays/specimens used to detect antibody levels.

Fig 2. Antibody response in participants with previous COVID-19 infection, vaccination, or both.

Anti-RBD antibodies were measured in (A) participants that had previous COVID-19 vaccines without self-reported prior infection. (B) Participants that did not have a prior infection and were divided into subgroups based on whether they had received a booster or not. (C) Participants that had a previous COVID-19 infection or COVID-19 vaccines or both. Participants were categorized by the vaccine or COVID-19 infection and the time interval from vaccination/infection to blood sample collection. (D) Participants were categorized based on the order and approximate time scale of COVID-19 infection and vaccination for each group. Cutoff defined per manufacturer. *P values are calculated by the Mann-Whitney test. *p-value <0.05, **p-value <0.01, ***p-value <0.001 and ****p-value <0.0001.

Fig 3. The correlation of sample types and assays.

(A) Venn diagrams showing overlap of positive results of (A) RBD of Spike and (B) NC from two different assays. (C) Correlation between the value of anti-RBD IgG by Beckman and the MSD assay. (D) Correlation between the value of total anti-NC by Bio-Rad assay and the value of anti-NC IgG by the MSD assay. (E) Correlation of the value of anti-RBD IgG between serum and saliva samples. (F) Correlation between the value of anti-RBD IgG using serum samples by the Beckman assay and using saliva samples by the MSD assay. A red dotted line indicates the cutoff line. All test values equal to or greater than this line is considered positive. r is calculated using Spearman correlation.