How Does an Annual Flu Shot Impact Response?

Annual influenza vaccination is prudent for people at high risk from complications and for people who live or work in places where people aggregate. Every health care system encourages its workers to receive an annual influenza vaccination. Unfortunately, not all health care workers are on board with the recommendation and vaccination coverage tends to be suboptimal.

A multinational team of infectious disease researchers has published an article that looks at the antibody response to influenza in 2 groups: health care workers who tend to be vaccinated consistently and annually, and health care workers who tend not to be vaccinated consistently. They called these groups the "high vaccination group" and the "low vaccination group," respectively.

This research is based on previous findings that individuals who are vaccinated frequently have reduced serological responses. However, it hasn't been clear if the reduced serological response translates to decreasing protection. These researchers included 202 health care workers, of whom, 192 were able to complete the study. A full 82% of the participants were considered highly vaccinated, and the remainder represented the low vaccination group.

Participants in the low vaccination group tended to have a greater than fourfold increase in influenza antibody titers after vaccination, and participants in the high vaccination group had a less robust response. The difference between the low vaccination group and the high vaccination group was not statistically significant. Titers in the low vaccination group remained elevated throughout the influenza season and in the months following.

The researchers were quick to acknowledge that none of the health care workers in the low vaccination group were completely unvaccinated, and all of them had been vaccinated at least once. The researchers also indicated that they were unable to determine if participants had actually contracted influenza in the past. If they had, previous infection could alter antibody response.

Despite the differences in influenza antibody titers, both groups had sufficient protective antibody titers after they were vaccinated. Participants in the high vaccination group tended to be less likely to develop influenza.

These findings do not in any way suggest that less frequent immunization is possible or safe. The researchers stress that influences on morbidity is sufficient reason to continue to vaccinate health care workers annually.

This article appears in the journal Vaccine.

Reference

Leung VK, Carolan LA, Worth LJ, et al. Influenza vaccination responses: Evaluating impact of repeat vaccination among health care workers. Vaccine. 2017;35(19):2558-2568.