In a cluster-randomized observational study, adults aged 50 to 64 years had a lower incidence of influenza when vaccinated with high-dose recombinant versus egg-based, standard-dose vaccines. “The incidence of PCR-confirmed influenza was 15.3% lower among those who received the recombinant vaccine than among those who received a standard-dose vaccine,” the authors of the real-world study conclude. “The evidence that the recombinant vaccine conferred more protection against influenza than standard-dose vaccines was strengthened by our cluster-randomized study design.”
During the 2018–2019 and 2019–2020 influenza seasons, Kaiser Permanente Northern California facilities routinely administered either a high-dose recombinant influenza vaccine (Flublok Quadrivalent) or 1 of 2 standard-dose influenza vaccines to adults 50 to 64 years of age (primary age group) and 18 to 49 years of age. Facilities alternated weekly between the 2 vaccines.
Based on a primary outcome of PCR-confirmed influenza A or B, the investigators found: “The study population included 1,630,328 vaccinees between the ages of 18 and 64 years (632,962 in the recombinant-vaccine group and 997,366 in the standard-dose group). During this study period, 1,386 cases of PCR-confirmed influenza were diagnosed in the recombinant-vaccine group and 2,435 cases in the standard-dose group. Among the participants who were 50 to 64 years of age, 559 participants (2.00 cases per 1,000) tested positive for influenza in the recombinant-vaccine group as compared with 925 participants (2.34 cases per 1,000) in the standard-dose group (relative vaccine effectiveness, 15.3%; 95% confidence interval [CI], 5.9 to 23.8; P = 0.002). In the same age group, the relative vaccine effectiveness against influenza A was 15.7% (95% CI, 6.0 to 24.5; P = 0.002). The recombinant vaccine was not significantly more protective against influenza-related hospitalization than were the standard-dose vaccines.”