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Prior DNA Priming Ups Influenza Vaccine Effectiveness

H5-DNA priming 24 weeks pre-H5N1 monovalent inactivated vaccine increases immune response

TUESDAY, Oct. 4 (HealthDay News) -- H5-DNA priming 24 weeks prior to H5N1 monovalent inactivated vaccine (MIV) is safe, enhances H5-specific antibody titers, and induces protective hemagglutination inhibition (HAI) titers, according to a study published online Oct. 4 in The Lancet Infectious Diseases.

Julie E. Ledgerwood, D.O., from the National Institutes of Health in Bethesda, Md., and colleagues evaluated the safety and immunogenecity of DNA encoding H5 as a primer to improve antibody responses to inactivated influenza vaccination in two studies (VRC-306 and VRC-310). A total of 59 healthy 18- to 60-year-old adults from VRC-306, and 20 from VRC-310 studies were randomized to receive intramuscular H5-DNA either at day zero or at day zero and week four, followed by H5N1-MIV at week four or 24. The antibody and T-cell responses were compared with two-dose regimens of H5N1-MIV at week four or 24.

The investigators found that H5-DNA priming was safe, and, following an H5N1-MIV boost, it enhanced H5-specific antibody titers, especially if the interval between DNA-prime and MIV-boost was extended to 24 weeks. In both the studies, protective HAI titers were observed in 81 percent of individuals with DNA priming with a 24-week MIV-boost interval, and the geometric mean titer rose more than four times that of individuals given only MIV-MIV regimen. The prime-boost regimen also induced neutralizing antibodies directed to conserved stem region of H5 in several individuals. There were no serious vaccine-related adverse events.

"A DNA-MIV vaccine regimen could enhance the efficacy of H5 or other influenza vaccines and shows that anti-stem antibodies can be elicited by vaccination in man," the authors write.

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