Studies: Statins May Mess With Flu Shot Efficacy

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Two new studies published in the Journal of Infectious Diseases implicate statin drugs in decreasing the efficacy of the seasonal influenza vaccines. About 32 million Americans are currently taking these cholesterol lowering medications. Under the most recent cholesterol guidelines almost half of Americans aged 40 to 75 qualify to take statins to lower their risk of heart disease. The Centers for Disease Control and Prevention (CDC) estimate that 40 percent of the 46 million Americans aged 65 years of age or older are taking statins to lower their cholesterol.

This study sheds light on a perfect storm of events. The flu season is officially here and older populations are not only more vulnerable to getting the flu but also are most likely to be taking a statin. According to the CDC's Influenza Hospitalization Surveillance Network the highest rate of hospitalization was among adults aged ¥65 years (13.4 per 100,000 population).

In one of the new studies conducted during the 2009-2010 and 2010-2011 flu seasons, researchers analyzed the immune response of 7,000 participants aged 65 and older to the flu vaccine. What they observed was significantly reduced levels of antibody formation against flu virus strains in statin users three weeks post vaccination. 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, said Dr. Steven Black, MD, of Cincinnati Children s Hospital Medical Center and lead author of this study.

The other study, conducted at Emory University, examined data spanning nine flu seasons from 2002 to 2011 that included information on 140,000 enrollees from a managed care in Georgia. The data reviewed included information about flu vaccination, statin prescriptions and cases of acute respiratory illnesses (though not confirmed as influenza) that required medical attention. What we found was a potential signal that the effectiveness of flu vaccine in older people may be somewhat compromised if they are on statins, compared to those who are not on statins, according to Saad B. Omer, MBBS, MPH, PhD, of Emory University and lead author of this study.

Before any panic ensues or anyone stops taking their statin medication, these studies serve as an impetus for further research. Instead, 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, according to Robert L. Atmar, MD, and Wendy A. Keitel, MD, of Baylor College of Medicine in Houston, the authors of an editorial commentary in the same journal.

It should be noted that in the very same journal a study published in 2011, it was concluded that statins may have anti-inflammatory properties that could reduce mortality from flu virus infections. This highlights how preliminary these data are and that they should not yet influence healthcare decision making.