Flu risk to patients requires more research, epidemiologists say.

Reviewers of four trials often used to support mandatory flu vaccination policies for long-term care workers say the benefits were overstated. But the lead researcher still says he recommends vaccination for healthcare workers. 

A group of epidemiologists from Canada, Australia and France looked at the math behind the previous randomized control trials and found calculations about patient outcomes, including mortality, were too good to be true.

“The impression that unvaccinated healthcare workers place their patients at great influenza peril is exaggerated,” wrote lead author Gaston De Serres, M.D., Ph.D., professor of epidemiology at Canada’s Laval University. “Instead, the attributable risk and vaccine-preventable fraction both remain unknown and the (number of vaccinations needed) to achieve patient benefit still requires better understanding.” 

Original predictions based on the principle of dilution were high enough that extrapolating them would mean healthcare worker vaccinations could prevent more flu deaths than happen in the entire U.S. each year. The review shows 6,000 to 32,000 hospital workers would need to be vaccinated before a single patient death could be averted.

While De Serres said the flu risk attributed to healthcare workers and the power of vaccine prevention remain unknown, he still recommends health professionals get vaccinated because data do not refute potential positives.