Influenza infection poses special challenges for solid-organ transplant recipients, as "the flu" increases their risk for bacterial pneumonia, admission to intensive care, and death. Furthermore, research suggests influenza infection can even increase the risk for allograft rejection and poorer allograft survival.

Providing an annual vaccination that contains 15 micrograms of antigen per viral strain is an effective preventative strategy in solid-organ transplant recipients. Now, the results of a new study show that high-dose vaccines possessing 60 micrograms antigen per influenza strain enhance vaccine immunogenicity in this population.

The use of vaccines with higher doses of antigen is an attractive strategy to improve the immunogenicity of influenza vaccination in transplant recipients. The effect of vaccination using a double-dose (DD) that contains 30 micrograms of antigen in these patients had not been studied.

The results of the new study, published in Vaccine, suggest that using a DD influenza vaccine is safe and that it might even increase antibody response in this population.

Assessing the Immunogenicity and Safety of Double-Dose Versus Standard Dose of Seasonal Influenza Vaccine in Transplant Recipients

In a randomized controlled trial, researchers compared the immunogenicity and safety of double-dose 30 micrograms with the standard dose (SD) of 15 micrograms influenza vaccine in kidney and liver transplant recipients.

The team used hemagglutination-inhibition assay to assess immunogenicity. They defined vaccine response as seroconversion to at one or more viral strains two weeks after vaccination and seroprotection as a titer ≥40.

They enrolled 63 kidney and 16 liver transplants into the study. Forty of the participants received the double dose and 39 received the standard vaccine. The members of both groups shared baseline characteristics.

The median time from kidney or liver transplantation was 23 months and 40 months in the standard-dose and double-dose, respectively. At 82.5 percent in the DD group and 79.5 percent in the SD group, most participants had received an influenza shot the previous year.

At 32.9 percent in the entire study population, vaccine response was generally poor and below the standard of efficacy (40 percent) as set by the European Medicines Agency. There was a minimal 14 percent increase in vaccine response rate with a slight trend towards enhanced immunogenicity.

Overall, 40 percent of those who had received the DD responded to the vaccine, compared with only 26 percent of those who had been given the standard dose. In those receiving the double-dose, more participants were seroprotected to all viral strains following vaccination.

Most adverse events occurring in both groups were mild; no severe adverse reactions associated with the vaccine were observed.

The authors concluded their study by saying, "While increasing the amount of antigens delivered with vaccination from 15 to 30 microgram did not significantly improve the pre-established definition for vaccine response, the observed trend toward a better immunogenicity with the double-dose vaccination is encouraging and adds more evidence for the use of high-dose influenza vaccine in solid-organ transplant."

The high-dose vaccine is currently available only in North America, so clinicians elsewhere might consider using two 15-microgram injections of the standard vaccine to increase the amount of influenza antigens, although this strategy has not been tested in solid-organ transplant recipients.