Compatibility of ASO3-adjuvanted H1N1pdm09 and seasonal trivalent influenza vaccines in adults: results of a randomized, controlled trial.

When Canada chose a novel adjuvanted vaccine to combat the 2009 influenza pandemic, seasonal trivalent inactivated vaccine (TIV) was also available but compatibility of the two had not been assessed. To compare responses after concurrent or sequential administration of these vaccines, adults 20-59 years old were randomly assigned (1:1) to receive ASO3-adjuvanted H1N1pdm09 vaccine (Arepanrix, GSK, Quebec City, Quebec), with TIV (Vaxigrip, Sanofi Pasteur, Toronto) given concurrently or 21 days later. Blood was obtained at baseline and 21 days after each vaccination to measure hemagglutination inhibition (HAI) titers. Adverse effects were assessed using symptom diaries and personal interviews. 282 participants completed the study (concurrent vaccines 145, sequential vaccines 137). HAI titers to H1N1pdm09 were ≥ 40 at baseline in 15-18% of participants and following vaccination in 91-92%. Initially seropositive subjects (titer ≥ 10) had lower H1N1pdm09 geometric mean HAI titers (GMT) after concurrent than separate vaccinations (320.0 vs 476.5, p=0.039) but both exceeded GM responses of initially naïve participants, which were unaffected by concurrent TIV. Responses to TIV were not lower after concurrent than separate vaccination. Adverse event rates were not increased by concurrent vaccinations above those with H1N1pdm09 vaccine alone. This adjuvanted H1N1pdm09 vaccine was immunogenic and compatible with concurrently administered TIV.