An experimental avian influenza A H7N9 vaccine prompted immune response in 59% of patients who received two injections at the lowest dosage tested, but only if the vaccine was mixed with an MF59 adjuvant. The study results were published in the Journal of the American Medical Association and the clinical trial is sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH).
In a multicenter, randomized, double-blind Phase 2 trial at four U.S. sites, 700 adults ages 19–64 received the H7N9 inactivated virus vaccine administered intramuscularly on days 0 and 21. Two groups received the vaccine at either 15mcg or 45mcg without adjuvant while the remaining five groups received the vaccine at 3.75mcg, 7.5mcg, or 15mcg. From these five groups, three groups received MF59 adjuvant with both inoculations and two received only one dose of adjuvant with their first or second injection of vaccine. A hemagglutination inhibition (HAI) antibody assay was used to assess the likelihood that the vaccine would provide protection against influenza disease at HAI levels of ≥40. Key HAI assays were performed on blood samples taken at 42 days following the first inoculation.
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Fifty-nine percent of the patients receiving two injections of the lowest vaccine dose and two doses of adjuvant exhibited HAI levels of ≥40. However, those who received 15mcg dose vaccines and one dose of adjuvant at the time of the first inoculation had antibody responses that were not significantly lower than those who received two doses of adjuvant. This suggests that one dose of adjuvant administered with the first vaccine dose may be sufficient to initiate a significant immune response. Those who received the vaccine without adjuvant, regardless of vaccine dose, had minimal immune responses.
Clinical trials such as this can help with preparedness in the event of an H7N9 avian influenza pandemic, states NIAID Directed Anthony S. Faicu, MD. If these results can be replicated in further clinical trials, adjuvant-sparing and vaccine antigen-sparing vaccine regimens could be utilized to allow for greater availability of the vaccine.
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