One-year follow-up of the immunogenicity and safety of a first and second booster dose of the NVX-CoV2373 (TAK-019) vaccine in healthy Japanese adults who had previously received a primary series of COVID-19 mRNA vaccine: Final report of a phase 3 open-label trial.

BACKGROUND

In this phase 3, single-arm, open-label trial in Japanese adults who had previously received a COVID-19 mRNA primary vaccination (NCT05299359), two NVX-CoV2373 boosters, administered 5 months apart in the main and extension parts of the study, respectively, induced robust immune responses up to day (D) 15 after each dose. This final report presents immunogenicity and safety findings at 1-year follow-up.

METHODS

Immunogenicity of the first NVX-CoV2373 booster (main part) and second NVX-CoV2373 booster (extension part) was assessed at D29, D91, D181, and D366 in each study part. Safety findings were evaluated for each study part at 1-year follow-up.

RESULTS

Of 150 participants who received a first NVX-CoV2373 booster on D1, 21 did not participate in the extension part and 17 completed the main part. In total, 129 participants received a second booster on extension day (ED) 1, and 121 completed the extension part. In the main and extension parts, anti-SARS-CoV-2 serum immunoglobulin G (IgG) responses to the boosters peaked on D29 and ED15, respectively; serum neutralizing antibody (nAb) responses to the boosters peaked on D15 and ED29, respectively. Serum IgG and nAb titres remained relatively high in both study parts throughout the 1-year follow-up compared with their pre-booster titres on D1 and ED1. There were no deaths or adverse events leading to study discontinuation at 1-year follow-up for both study parts. A SARS-CoV-2 infection was reported in 14.0 % (21/150) of participants in the main part and 10.9 % (14/129) in the extension part; all cases were mild/moderate in severity.

CONCLUSION

The two NVX-CoV2373 boosters induced durable anti-SARS-CoV-2 immune responses up to 1 year after each dose and are therefore expected to persistently protect against SARS-CoV-2 infections and severe disease outcomes in Japanese adults. No new safety concerns were identified, demonstrating the expected acceptable safety profile in healthy Japanese participants.