While further research is needed to confirm the findings, this may have implications for the care of millions of people. More than 40 percent of Americans over the age of 65 take statins.
Both studies, published in The Journal of Infectious Diseases, found that people taking the cholesterol-lowering drugs had a significantly reduced immune response to influenza vaccination compared to those not taking statins. This could affect future flu shot recommendations and/or statin use around the time of vaccination in the elderly, experts say.
In the first study, researchers analyzed data on immune responses from an earlier flu vaccine clinical trial that took place during the 2009-2010 and 2010-2011 flu seasons. They looked at the potential effect of statin use on patients' initial immune responses after getting a flu shot. The analysis included nearly 7,000 adults over the age 65 in four countries, including the United States.
Both this new study and the original trial were funded by Novartis, a pharmaceutical company based in Switzerland that makes a flu vaccine for seniors that contains a compound called adjuvant, which amplifies its effect. Novartis's vaccine is licensed in Europe but not yet in the U.S.
After measuring the level of antibodies to the flu vaccine strains in patients' blood three weeks after getting the shot, the researchers concluded that statin users had a significantly reduced immune response to the vaccine compared to those not taking the drug. The effect was stronger in people taking synthetic statins as opposed to naturally derived varieties of the drug.
"Apparently, statins interfere with the response to influenza vaccine and lower the immune response, and this would seem to also result in a lower effectiveness of influenza vaccines," Dr. Steven Black of Cincinnati Children's Hospital Medical Center, the lead author of the immune response study, said in a statement.
In the other new study, researchers from Emory University looked at the possible impact of statin use on the effectiveness of the flu vaccine in preventing serious respiratory illnesses. They analyzed data on nearly 140,000 people spanning nine flu seasons from 2002 to 2011, including information about flu vaccination, statin prescriptions and cases of acute respiratory illness.
After the investigators adjusted for other factors, the results showed that vaccine effectiveness for preventing serious respiratory illness was lower among patients taking statins compared to those who were not on statins, particularly when flu was widespread in the state.
If confirmed, the findings could change recommendations for flu immunization in seniors, with preference for a high-dose flu vaccine to counteract the apparent effect of statins, the researchers suggest.
Currently, a high-dose flu vaccine is approved for adults 65 and older in the U.S., as are several standard dose vaccines, but the CDC has not expressed a preference for which vaccine seniors should get.
The CDC recommends that everyone 6 months of age and older get a flu shot every year. Older adults are at higher risk for serious illness and complications from the flu, including death.
Another option, if the statin-effect were proven, might be to have statin users stop taking the drug around the time of vaccination, though researchers would need to figure out for how long and if this would be effective.
But while the findings of both studies raise important questions, Robert L. Atmar, M.D., and Wendy A. Keitel, M.D., of Baylor College of Medicine in Houston, point out in an accompanying commentary that they should not yet affect how physicians care for their patients.
"There is a clear-cut benefit to persons taking statins, so patients should not stop statin use because of the study results, even for a short time," Atmar told HealthDay.
Rather, he and Keitel wrote in the commentary that "the results of these studies should be viewed as hypothesis-generating and should prompt further investigations into whether statins reduce inactivated influenza vaccine immunogenicity, and, if so, the mechanisms by which immune responses and associated vaccine effectiveness are adversely affected."