Serum antibodies against circulating influenza strains among vaccinated and unvaccinated general practitioners during two consecutive years (2002-2003).

Efficacy studies have not answered the question whether influenza vaccination among general practitioners (GPs) has a substantial additive effect on their immunity. To evaluate this effect the influenza antibody titres in vaccinated and unvaccinated GPs were compared in a controlled trial during two consecutive winter periods (2002-2003 and 2003-2004). The seroprotection rates against the circulating A/H3N2 influenza virus amount to 80% and 42% in the unvaccinated group in 2002 and 2003, respectively. In the vaccinated GPs the seroprotection rate increases from 91% to 96% in 2002 and from 70% to 83% in 2003 after vaccination. Besides vaccination, the (high) basic antibody titre before vaccination and working in a child and family preventive medicine unit were predicting a protective antibody level in GPs.