Randomized, Open-Label Phase 3 Study Evaluating Immunogenicity, Safety, and Reactogenicity of RSVPreF3 OA Coadministered with FLU-QIV-HD in Adults Aged ≥ 65

Respiratory syncytial virus (RSV) and influenza pose major disease burdens in older adults due to an aging immune system and comorbidities; seasonal overlap exists between these infections. In 2023, the RSV prefusion protein F3 older adult (RSVPreF3 OA) vaccine was first approved in the USA as a single dose for prevention of lower respiratory tract disease due to RSV in adults aged ≥ 60 years. The vaccine has since been approved in the European Union and elsewhere. RSVPreF3 OA and FLU-QIV-HD could be coadministered if immunogenicity, safety, and reactogenicity are not affected. This open-label, randomized (1:1), controlled, phase 3 study in 1029 adults aged ≥ 65 years in the USA evaluated the immunogenicity (up to 1 month after last vaccine dose) and safety (up to 6 months after last vaccine dose) of RSVPreF3 OA coadministered with FLU-QIV-HD (co-ad group) versus FLU-QIV-HD alone followed by RSVPreF3 OA at a separate visit 1 month later (control group). Non-inferiority criterion was defined as an upper limit of the two-sided 95 Adults aged 65 years or older are vulnerable to infections caused by influenza and respiratory syncytial viruses, due to an aging immune system and other underlying conditions. Infections with both viruses increase during autumn and winter seasons in temperate climates. In 2023, a vaccine against respiratory syncytial virus, called RSVPreF3 OA, was first approved for use in adults aged 60 years or older in the USA; the vaccine has since also been approved in the European Union and elsewhere. Giving RSVPreF3 OA in the same vaccination visit (coadministration) with a high-dose influenza vaccine, called FLU-QIV-HD, which is given to adults aged 65 years or older, could help protect against both respiratory syncytial virus and influenza. This article reports the results of a phase 3 trial comparing coadministration of the RSVPreF3 OA and FLU-QIV-HD vaccines with sequential administration (FLU-QIV-HD followed by RSVPreF3 OA 1 month later) in 1029 adults aged 65 years or older in the USA. Proportions of participants across age categories between groups, and the proportions of male (50.4