Background: The immunogenicity of the standard influenza vaccine is reduced in solid-organ transplant (SOT) recipients, so that new vaccination strategies are needed in this population.

Methods: Adult SOT recipients from nine transplant clinics in Switzerland and Spain were enrolled if they were >3 months after transplantation. High, with stratification by organ and time from transplant. The primary outcome was vaccine response rate, defined as a ≥4-fold increase of hemagglutination-inhibition titers to at least one vaccine strain at 28 days post-vaccination. Secondary outcomes included PCR-confirmed influenza and vaccine reactogenicity.

Results: 619 patients were randomized, 616 received the assigned vaccines, and 598 had serum available for analysis of the primary endpoint (standard, n=198; MF59-adjuvanted, n=205; high-dose, n=195 patients). Vaccine response rates were 42% (84/198) in the standard vaccine group, 60% (122/205) in the MF59-adjuvanted vaccine group, and 66% (129/195) in the high-dose vaccine group (difference in intervention vaccines vs. standard vaccine, 0.20 [97.5% CI 0.12-1]; p<0.001; difference in high-dose vs. standard vaccine, 0.24 [95% CI 0.16-1]; p<0.001; difference in MF59-adjuvanted vs. standard vaccine, 0.17 [97.5% CI 0.08-1]; p<0.001). Influenza occurred in 6% the standard, 5% in the MF59-adjuvanted, and 7% in the high-dose vaccine groups. Vaccine-related adverse events occurred more frequently in the intervention vaccine groups, but most of the events were mild.

Conclusions: In SOT recipients, use of an MF59-adjuvanted or a high-dose influenza vaccine was safe and resulted in a higher vaccine response rate.