Two new studies published in the Journal of Infectious Diseases offer preliminary evidence that the flu vaccine may not work as well in people taking statins. But there is widespread agreement among experts that the association, much less a demonstration of cause and effect, has not been proven, and that current clinical practice should not be changed because of the findings.
In one paper, a retrospective analysis of data from a randomized controlled trial of different flu vaccines, people taking statins had a smaller immune system response to the vaccines compared to people not taking statins.
In the second paper, a retrospective analysis of data from a large managed care organization, following a flu vaccination people who took statins were more likely than non-statin users to develop an acute respiratory illness during the flu season, suggesting that the vaccine was less effective in them.
In both studies, however, there were large and important differences between statin users and nonusers. Although the researchers attempted to adjust for these differences, ultimately the trials are “hopelessly confounded by indication,” said Jacob Udell (University of Toronto), who has studied the effect of flu vaccine in cardiovascular patients.
“I really don’t believe the hypothesis is plausible,” said Udell, pointing to the absence of “an epidemic of influenza outbreaks just among statin users.” Udell and another researcher, Orly Vardeny (University of Wisconsin) speculate that a reduced immune response in these patients is not due to the statins but the underlying comorbidities of diabetes, obesity, and cardiovascular disease, among others.
Vardeny also pointed out that the first study had a major flaw in that the investigators were unable to adjust for prior vaccinations, which is known to have a major effect on immune response.
Others believe the hypothesis is plausible. In an accompanying editorial, Robert Atmar and Wendy Keitel (Baylor College) write that the findings “are biologically plausible, based on known immunomodulatory effects of these drugs, and raise important questions about the use of these important medications.” But, they continue, the results should not influence or change the way physicians care for patients. “Should statins be stopped for a period while influenza vaccine is administered? Should IIV [inactivated influenza vaccine] not be administered to statin users? In our opinion, the answer to all of these questions is no. Instead, the results of these studies should be viewed as hypothesis generating and should prompt further investigations…”