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Updated: May 11, 2026

An Optimized Hemagglutination Inhibition (HI) Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Prime-boost interval matters: a randomized phase 1 study to identify the minimum interval necessary to observe the H5
Julie E Ledgerwood1, Kathryn Zephir, Zonghui Hu
1Vaccine Research Center, National Institute ofAllergy and Infectious Diseases, National Institutes of Health, Bethesda,MD 20892, USA. ledgerwood@mail.nih.gov
Background:
H5 DNA priming was previously shown to improve the antibody response to influenza A(H5N1) monovalent inactivated vaccine (MIV) among individuals for whom there was a 24-week interval between prime and boost receipt. This study defines the shortest prime-boost interval associated with an improved response to MIV.
Methods:
We administered H5 DNA followed by MIV at intervals of 4, 8, 12, 16, or 24 weeks and compared responses to that of 2 doses of MIV (prime-boost interval, 24 weeks).
Results:
H5 DNA priming with an MIV boost ≥12 weeks later showed an improved response, with a positive hemagglutination inhibition (HAI) titer in 91% of recipients (geometric mean titer [GMT], 141-206), compared with 55%-70% of recipients with an H5 DNA and MIV prime-boost interval of ≤8 weeks (GMT, 51-70) and 44% with an MIV-MIV prime-boost interval of 24 weeks (GMT, 27).
Conclusion:
H5 DNA priming enhances antibody responses after an MIV boost when the prime-boost interval is 12-24 weeks. Clinical Trials Registration. NCT01086657.
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