Safety, immunogenicity, and efficacy of a COVID-19 vaccine (NVX-CoV2373) co-administered with seasonal influenza vaccines: an exploratory substudy of a randomised, observer-blinded, placebo-controlled, phase 3 trial

Background: Safety and immunogenicity of COVID-19 vaccines when co-administered with influenza vaccines have not yet been reported. Methods: A sub-study on influenza vaccine co-administration was conducted as part of the phase 3 randomised trial of NVX-CoV2373’s safety and efficacy; ~400 participants meeting main study entry criteria, with no contraindications to influenza vaccination, were enroled. After randomisation to receive NVX-CoV2373 or placebo, sub-study participants received an open-label influenza vaccine at the same time as the first dose of NVX-CoV2373. Reactogenicity was evaluated for 7 days post-vaccination plus monitoring for unsolicited adverse events (AEs), medically-attended AEs (MAAEs), and serious AEs (SAEs). Vaccine efficacy against COVID-19 was assessed. Findings: Sub-study participants were younger (median age 39; 6.7 % ≥65 years), more racially diverse, and had fewer comorbid conditions than main study participants. Reactogenicity events more common in co-administration group included tenderness (70.1% vs 57.6%) or pain (39.7% vs 29.3%) at injection site, fatigue (27.7% vs 19.4%), and muscle pain (28.3% vs 21.4%). Rates of unsolicited AEs, MAAEs, and SAEs were low and balanced between the two groups. Co-administration resulted in no change to influenza vaccine immune response, while a reduction in antibody responses to the NVX-CoV2373 vaccine was noted. Vaccine efficacy against COVID-19 was 87.5% (95% CI: -0.2, 98.4) in those 18-<65 years in the sub-study while efficacy in the main study was 89.8% (95% CI: 79.7, 95.5).  Interpretation: This is the first study to demonstrate safety, immunogenicity, and efficacy of a COVID-19 vaccine when co-administered with influenza vaccines

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