Study Objectives
SARS-CoV-2 has infected more than 150 million and caused over 3 million deaths. While development of vaccines will likely temper the associated morbidity and mortality, the long-term durability of the immune response to these vaccines remains unknown. Our objective was to evaluate the use of a rapid IgM/IgG SARS-CoV-2 antibody detection kit as a screening tool for humoral immune response to COVID-19 vaccination and to assess neutralizing and nucleocapsid antibodies via ELISA.
Methods
We conducted a cross-sectional study of pediatric health care workers (PHCW), with no history of SARS-CoV-2 infection who received 2 doses of BNT162b2 (n=113) or mRNA-1273 (n=12), at a pediatric quaternary care institution. Participants were tested for IgM/IgG antibodies to the SARS-CoV-2 spike protein receptor-binding domain with the Hangzhou Biotest Biotech RightSign COVID-19 IgG/IgM Rapid Test Cassette. ELISAs were subsequently run to detect the presence of anti-spike IgG/neutralization effect and IgM/IgG SARS-CoV-2 anti-nucleocapsid antibodies. The mean number of days post 2nd dose was 22, the range was 17-36.
Results
98.4% received positive rapid IgG results; 0.8% were IgM+. Of those with rapid IgG+ results, 100% were anti-spike protein IgG+ on ELISA; none who tested IgG negative via the rapid test demonstrated positive anti-spike protein IgG on ELISA. All those with positive rapid tests demonstrated neutralizing capability via ELISA. With respect to anti-nucleocapsid antibodies, only 1.6% were IgM+ and 5.6% were IgG+.
Conclusion
Anti-spike serology was consistent with previous studies. In many countries, HCWs were among the first to be vaccinated and several larger studies have explored the vaccine-mediated antibody responses in this population. However, to our knowledge there have been no studies examining PHCW. This population is unique in that due to their work with children, they are likely more frequently exposed to coronaviruses than the general population. Both the spike protein and the nucleocapsid protein appear somewhat conserved across coronaviruses, and children with no exposure to/history of SARS-CoV-2 infection have been shown to have detectable levels of IgG antibodies reactive to the SARS-CoV-2 spike protein. However, very few participants in our study were anti-nucleocapsid IgM+/IgG+; the significance is as yet undetermined. Although the generalizability of our results may be limited due to the limited number who received mRNA-1273, the strong correlation between the rapid results and confirmatory ELISA testing suggests this test may be used to assess for positive and neutralizing antibody response to BNT162b2. This may allow for rapid and relatively inexpensive documentation and monitoring of individual immune response, including evaluating the need for booster vaccination, as well as aiding in large-scale immune surveillance.