Change in titer of IgG antibodies to N-protein of SARS-CoV-2 (Stage IIb);Frequency of symptomatic COVID-19 with laboratory-confirmed infection within 6 months after vaccination compared with the placebo group (Stage III)

Change in titer of IgG antibodies to N-protein of SARS-CoV-2 (Stage IIb);Frequency of symptomatic COVID-19 with laboratory-confirmed infection within 6 months after vaccination compared with the placebo group (Stage III)