[The efficacy and problems with influenza vaccination among hospital workers]

The purposes of this study were: (1) to assess the therapeutic and side effects of influenza vaccination during a winter season by comparison of vaccinated and non-vaccinated subjects; and (2) to survey their willingness to receive vaccination in the future based on their experience with the present vaccination.

The subjects were 185 vaccinated hospital workers and 450 unvaccinated city office workers. We explained to the first group the desirability of receiving vaccination for the purpose of preventing in-hospital infections and received informed consent before administering influenza vaccinations. There were five subjects who did not receive any vaccination due to strong side effects from previous vaccinations or who did not give consent. We then examined the therapeutic and side effects of the vaccination with the vaccinated subjects. A questionnaire was also filled out by both groups of subjects regarding their physical condition and whether they wished to receive vaccination in the future. In this study, the criterion for influenza was a fever of 38.5 degrees C or higher while common cold was concluded with a fever under 38.5 degrees C.

The percentage of subjects who subsequently developed influenza symptoms was 13.2% for the vaccinated group whereas that for the unvaccinated group was 33.2%. The difference was significant (P < 0.01). There was no significant difference in the frequency of common cold symptoms between the two groups. According to the vaccinated group's self-report (through the questionnaire; n = 159), 16 subjects (10%) suffered some kind of side effects after the vaccination. In terms of their desire to receive vaccination the following year, in the vaccinated group, 25% of those who reported side effects wanted vaccination the following year whereas 86% of those who did not report side effects wanted vaccination. The difference was significant (P < 0.01).

The significantly lower percentage of vaccinated subjects with influenza symptoms may have been due to the vaccination effect. The prevalence of side effects (10%) was rather low. Although a relatively high percentage of the vaccinated subjects wished to receive vaccination in the following year, the breakdown indicated that only a small number of those with side effects wanted furture vaccination. Even among those with no side effect, there were some (9.1%) who did not desire vaccination in the future. Thus, there seems to be a need for further education regarding the importance of preventing influenza through vaccination.