Two doses of influenza vaccine improve effectiveness in solid organ transplant recipients

Administering a second dose of influenza vaccine 5 weeks after the initial vaccination made influenza vaccines more effective among patients who had received a solid organ transplant, according to researchers in Spain.

“Solid organ transplant recipients are at higher risk for acquiring influenza infection with worse morbidity outcomes. Annual inactivated trivalent influenza vaccination is internationally recommended, and it is the most effective strategy for reducing the incidence and complications of influenza disease in solid organ transplant recipients,” Elisa Cordero, MD, of the clinical unit of infectious diseases, microbiology and preventive medicine at the Institute of Biomedicine of Seville, Spain, and colleagues wrote. “However, the immunological response to the influenza vaccine is heterogeneous in this population, with rates of seroprotection that range from 15% to 90%, generally lower than those of healthy individuals.”

Cordero and colleagues performed a phase 3, randomized, controlled, multicenter, open-label clinical trial on 499 patients who had received solid organ transplants. Patients were randomly assigned to receive either one dose (control group) or two doses (booster group) of influenza vaccine, administered 5 weeks apart.

Ten-week seroconversion did not meet significance in the modified intent-to-treat population, the researchers wrote. However, the booster group had higher seroconversion rates for the per-protocol population — 53.8% vs. 37.6% for influenza A(H1N1) pdm; 48.1% vs. 32.3% for influenza A(H3N2) and 90.7% vs. 75% for influenza B; P < .05.

Cordero and colleagues wrote that the booster group also had higher rates of seroprotection at 10 weeks — 54% vs. 43.2% for A(H1N1)pdm; 56.9% vs. 45.5% for A(H3N2) and 83.4% vs. 71.8% for influenza B; P < .05. Both groups had similar clinical efficacy (99.2% vs. 98.8%) and serious adverse event rates (6.4% vs. 7.5%). A total of five patients from across groups were diagnosed with influenza at 3 to 6 months after vaccination (0.8% control group vs. 1.2%).

The study was limited by the fact that researchers did not perform any routine biopsies, meaning some asymptomatic infections may have gone undiagnosed, and by the very small number of lung transplant recipients.

“In summary, this is the first randomized controlled trial that reports a vaccination strategy that improves immunological effectiveness of influenza vaccination in solid organ transplant recipients,” the researchers wrote. “The safety and relevance of these results, with a number needed to treat for seroconversion and seroprotection below 10 patients, generate good-quality evidence to support the seasonal use of two doses of the influenza vaccine in solid organ transplant recipients beyond the first month after transplantation.” – by Andy Polhamus

Disclosure: The researchers report no relevant financial disclosures.