Abstract
Objective: For the management of novel coronavirus disease 2019 (COVID-19), antibody tests have been developed targeting the SARS-CoV-2 nucleocapsid protein (N antigen) and spike protein S1 domain (S antigen). In this study, we measured the N and S antibody titers before and after coronavirus vaccination in members of a sports club that had a COVID-19 outbreak and compared them to those of a sports club that did not have an outbreak at the same university. Furthermore, we investigated the characteristics of the two antibodies.
Subjects and methods: The subjects were 118 A club members that had an outbreak (44 PCR test positives) and 105 B club members that did not have an outbreak (1 PCR test positive). Serum was collected before vaccination and about 1 month after the second vaccination. Significance was assessed using the Mann-Whitney U test.
Results: In A club, the median S antibody titer before vaccination in PCR-positive subjects was 121 U/mL, and that in PCR-negative subjects was 0.4 U/mL (P < 0.001). After vaccination, the median S antibody titer in PCR-positive subjects increased to 38,198 U/mL, which was significantly higher than that in PCR-negative subjects (median: 5,164 U/mL) (P < 0.001). Post-vaccination S antibody titers in all subjects of both clubs were 15 U/mL or more, indicating effective production of neutralizing activity. Before vaccination, 61 A club and 6 B club members were positive for N antibodies. All 45 PCR-positive individuals from both clubs were N antibody-positive. On the other hand, among those who were PCR-negative or not tested, 17 from A club and 5 from B club were positive for N antibody. Pre-vaccination N antibody-positive subjects showed significantly higher post-vaccination S antibody titers than N antibody-negative subjects (P < 0.001).
Conclusion: Our findings suggest that SARS-CoV-2-infected persons generate high S antibody titers after vaccination. As all PCR-positive subjects were N antibody-positive, this antibody is useful for recognizing SARS-CoV-2-preinfected individuals. The presence of PCR-negative and N-antibody-positive patients suggest that multiple PCR tests are necessary for the diagnosis of COVID-19.
