Immunogenicity and safety of heterologous booster with protein-based COVID-19 vaccine (NVX-CoV2373) in healthy adults: A comparative analysis with mRNA vaccines.

Background: Information on the protein-based severe acute respiratory syndrome (SARS-CoV-2) vaccine-NVX-CoV2373 (Novavax), as a heterologous booster remains limited. We investigated the immunogenicity and adverse events of NVX-CoV2373 as a second booster and compared them with those of mRNA vaccines in healthy adults.

Methods: Healthcare workers who had received an mRNA vaccine (mRNA-1273 or BNT-162b2) as the first booster (third dose) 12 weeks prior were recruited. Participants voluntarily received either NVX-CoV2373 or an mRNA vaccine as a second booster. Participants with a history of SARS-CoV-2 infection were excluded. The primary outcomes included serum anti-SARS-CoV-2 spike protein (SP) and neutralizing antibody titers against B.1.1.7 (Alpha), B.1.1.529 (Omicron) BA2, and BA5 variants on the 28th day after the boost. Secondary outcomes included new SARS-CoV-2 infections and adverse events reported during the study period.

Results: A total of 160 participants were enrolled in this study. Compared with the mRNA vaccination group (n = 59), the NVX-CoV2373 vaccination group (n = 101) had significantly lower anti-SARS-CoV-2 SP antibody titers and neutralizing antibody titers against all variants tested after the boost. During the study period, higher rates of new SARS-CoV-2 infections and a lower incidence of adverse events were observed in the NVX-CoV2373 vaccination group. No significant differences in cellular immune responses were observed between the two groups.

Conclusions: Compared to a homologous mRNA booster vaccination, heterologous boosters with NVX-CoV2373 showed lower antibody responses, a higher incidence of new SARS-CoV-2 infections, and fewer adverse events.