HealthDay News – Two strategies, immunologic priming and mixing an experimental vaccine with MF59, may help curb the threat of a future avian flu pandemic, results of two separate studies published in The Journal of the American Medical Association suggest.
To compare safety and immunogenicity of different doses of influenza A/Shanghai/2/3 (H7N9) vaccine mixed with or without the MF59 adjuvant, Mark J. Mulligan, MD, of Emory University in Atlanta, and colleagues conducted randomized, double-blind phase 2 trials involving 700 patients aged 18 to 64 years.
On its own, the experimental vaccine produced a minimal immune response against H7N9, but when mixed with MF59, the vaccine created a significant immune response in 59% of patients. Younger participants responded even better, added the investigators; nearly 80% of the younger third of patients, aged 19 to 34 years, mounted an effective immune response.
In a separate study, Robert B. Belshe, MD, of the Saint Louis University School of Medicine in St. Louis, and colleagues assessed immunologic priming (the initial presentation of an antigen to allow antibody responses on revaccination) in the older avian influenza A/Vietnam/1203/2014 (H5N1) (Vietnam) vaccine when directed against the more contemporary H5N1 avian influenza virus, influenza A/Anhui/01/2005 (Anhui).
“The need to respond quickly to potential influenza pandemics is important. Immunologic priming with vaccine … directed toward an older avian influenza H5 strain might lead to secondary antibody responses to a single dose of more current H5 avian influenza vaccine,” wrote the scientists.
Randomized clinical trials beginning in June 2011 examined the effects of vaccine priming on healthy adult patients who were vaccinated one year previously with the Vietnam vaccine (n=72) and vaccine-naive patients (n=565).
Participants who were previously vaccinated with 90 µg of unadjuvanted Vietnam vaccine were randomly assigned to receive 3.75 µg of avian influenza Anhui vaccine with or without MF59 adjuvant, stratified by one versus two previous doses (one dose: n = 18 with MF59 and n = 17 without; two doses: n = 19 with MF59 and n = 18 without).
“Previous receipt of a single dose of influenza A (H5N1) Vietnam vaccine was associated with sufficient immunologic priming to facilitate antibody response to a different H5N1 antigen using low-dose Anhui (booster) vaccine,” concluded the researchers.