Main idea: All vaccination regimens were found to be safe and tolerable. While there were no overall differences between regimen intradermal injection of IIV3, and double injection of IIV3 by intramuscular route, showed higher responses compared to the other same-route regimens.
Seasonal influenza results in significant morbidity and mortality worldwide, but the currently licensed inactivated vaccines generally have low vaccine efficacies and could be improved.
Between August 17, 2012, and January 25, 2013, four sites enrolled healthy adults aged 18-70 years. Subjects were randomized to receive one of the following vaccination regimens: trivalent hemagglutinin (HA) DNA prime followed by trivalent inactivated influenza vaccine (IIV3) boost with a 3.5-month interval (DNA-IIV3), IIV3 prime followed by IIV3 boost with a 10-month interval (IIV3-IIV3), or concurrent DNA and IIV3 prime followed by IIV3 boost with a 10-month interval (DNA/IIV3-IIV3). Each regimen was additionally stratified by an IIV3 administration route of either intramuscular (IM) or intradermal (ID).
Results: Three hundred and sixteen subjects were enrolled. Local reactogenicity was mild to moderate in severity, with higher frequencies recorded following DNA vaccine administered by Biojector compared to IIV3 by either route (p <0.02 for pain, swelling, and redness) and following IIV3 by ID route compared to IM route (p <0.001 for swelling and redness). Systemic reactogenicity was similar between regimens. Though no overall differences were observed between regimens, the highest titers post boost were observed in the DNA-IIV3 group by ID route and in the IIV3-IIV3 group by IM route.