Randomized, placebo-controlled double blind study on the efficacy of influenza immunization on absenteeism of health care workers

Background. In healthy adults influenza immunization reduces absenteeism caused by respiratory infections, but data on its efficacy among health care workers are scarce. Objective. To determine the effect of the conventional inactivated influenza A vaccine on reducing absenteeism related to respiratory infections among pediatric health care providers. Study design. A randomized, placebo-controlled, double blind study on vaccine efficacy was conducted in two pediatric hospitals during the winter season 1996 to 1997, The primary endpoint was days of work lost from the hospital because of respiratory infections. The documentation of absenteeism was based on personal sickness logs. Results, Of the 547 randomized vaccinees 427 (78%) persons completed the 4-month follow-up and returned the sickness logs. Immunization failed to reduce episodes of respiratory infections (1.8 episodes/study period among vaccinees vs. 2.0 among controls). Similarly the vaccine failed to affect the total number of days the vaccinees suffered from respiratory infections (13.5 days vs. 14.6 days, respectively). However, days of work lost because of respiratory infections (1.0 days vs. 1.4 days, respectively, P = 0.02) and especially total numbers of days the study persons felt themselves unable to work when either on or off duty (2.5 days vs, 3.5 days, P 0.02) were significantly decreased. Conclusion. Influenza vaccination reduced absenteeism related to respiratory infections by 28%. We therefore believe that routine annual influenza immunizations should be recommended to health care providers working in pediatric settings.