Abstract
In the Netherlands, people indicated for seasonal influenza vaccination are divided in 3 risk groups, i.e. those less than 60 y (y) with comorbidity and those 60 y and over with and without comorbidity. Those risk groups were also eligible for pandemic vaccination during the 2009 influenza A(H1N1) pandemic. We assessed tolerability of seasonal influenza vaccination and 2 doses of pandemic influenza A(H1N1) vaccine, adjuvanted with MF-59, administered 2 and 5 weeks after seasonal 2009-2010 vaccination among adults. Vaccinees were asked to return questionnaires on local and systemic adverse events (AEs) after each of 3 consecutive vaccinations given at the office of their General Practitioner. Sex- and risk group-specific AE-frequencies were calculated. Generalized Linear Mixed Model with seasonal vaccination as reference was used to calculate odds ratios (ORs) for AEs of the 2 pandemic doses. 5553 questionnaires (3251 vaccinees) were returned. Vaccinees reported any local AE after seasonal vaccination and both pandemic doses in 34%, 23%, and 18%, respectively. These percentages were 29%, 25%, and 16% for any systemic AE. Men reported fewer local and systemic AEs then women (p<0.0001). The risk of local (OR range 0.34-0.63) and systemic (OR range 0.39-0.99) AEs (overall, stratified by risk group and by sex) was lower after both pandemic doses compared to seasonal vaccination. This decreased risk was more pronounced after the second pandemic dose than after the first. Therefore, we conclude that MF59-adjuvanted pandemic vaccine given after seasonal vaccination was well tolerated.