OBJECTIVES: There is conflicting evidence as to whether the combined administration of two vaccines can lead to poorer immunogenicity and reactogenicity. The co-administration of the Omicron-adapted COVID-19 vaccine from Novavax (NVX-CoV2601) and a 20-valent pneumococcal conjugate vaccine (PCV20) has not been previously investigated. METHODS: In this randomised, double-blind, placebo-controlled, non-inferiority trial, immunocompetent participants aged ≥60 years were randomised in a 1:1:1:1 ratio to four groups: NVX-CoV2601 plus PCV20 (combination group)
NVX-CoV2601 plus placebo (NVX-only group)
PCV20 plus placebo (PCV20-only group)
or placebo plus placebo (placebo group). The primary outcome was Omicron-specific anti-spike protein IgG ELISA units at day 28 in the combination group compared with the NVX-only group. Non-inferiority was established if the lower limit of the two-sided 95% CI of the geometric mean titre ratio was above the non-inferiority margin of 0.67. Secondary outcomes included anti-pneumococcal capsular polysaccharide (PCP) IgG ELISA units. Solicited local and systemic adverse events were collected for 7 days after vaccination. This study was registered with ClinicalTrials.gov, number NCT05767606, and the EU Clinical Trials Register, EudraCT number 2022-004118-12. RESULTS: All 256 randomised participants completed the study. The baseline characteristics were similar in the four groups. Overall, the median age was 64 (IQR 61 to 69) and 105 (41%) of 256 were male. At day 28, the geometric mean anti-spike protein IgG ELISA units were 534 U/mL (95% CI 432-660) in the combination group and 556 U/mL (95% CI 460-672) in the NVX-only group, resulting in a geometric mean titre ratio of 0.96 (95% CI 0.73-1.27), thereby meeting the criteria for non-inferiority. Anti-PCP IgG ELISA units at day 28 were 507 U/mL (95% CI 416-619) in the combination group and 592 U/mL (95% CI 485-723) in the PCV20-only group. Local and systemic reactogenicity was similar in the three active treatment groups. No safety concerns or serious adverse events were observed. CONCLUSIONS: Immunogenicity following co-administration of NVX-CoV2601 with PCV20 was non-inferior to administration of NVX-CoV2601 alone. Given the similar safety and reactogenicity profile, our findings may help to overcome concerns about concomitant vaccination and pave the way for combination vaccines. FUNDING: Novavax.