More than 40% of over-65s in the US use statins to control cholesterol, but two new studies suggest that statin use decreases the effect of the flu vaccine, according to findings published in The Journal of Infectious Diseases.

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People who take statins may find that their flu vaccine is less effective.

A high-dose flu vaccine is one of several standard-dose vaccines approved for adults over 65 in the US. The Centers for Disease Control and Prevention (CDC) recommend that everyone be vaccinated against flu every season from the age of 6 months. Seniors are at particular risk for serious illness and complications from flu, including death.

However, one of the new reports shows that many senior statin users had a significantly reduced immune response to the vaccination, compared with those not taking statins. In the other study, effectiveness at preventing serious respiratory illness was lower among patients taking statins.

One group of researchers analyzed immune response data from an earlier flu vaccine clinical trial conducted during the 2009-10 and 2010-11 flu seasons.

They focused on the potential effect of statin use on patients' initial immune responses after being immunized against flu. The study involved nearly 7,000 adults over the age 65 in four countries, including the US.

Reduced immune response in statin users

Statin users were found to have a significantly reduced immune response to vaccination compared with those not taking statins, as measured by the level of antibodies to the flu vaccine strains in patients' blood 3 weeks after vaccination.

Fast facts about flu
  • 70% of Americans aged 65 and over have had a flu vaccine in the last 12 months
  • 3,697 people died from flu in the US in 2013
  • The mortality rate for the US is 1.21 people in every 100,000.

Learn more about flu

The effect was most dramatic in patients on synthetic rather than naturally derived statins.

If confirmed, the findings could support the use of high-dose flu vaccine or vaccines containing adjuvants to boost immune response in older people.

Vaccines containing adjuvants have already been approved in Europe, but not yet in the US.

In the vaccine effectiveness study, researchers from Emory University in Atlanta, GA, investigated the possible impact of statin therapy on the effectiveness of the flu vaccine at preventing serious respiratory illness.

They analyzed data spanning nine flu seasons from 2002-11, including information about flu vaccination, statin prescriptions and cases of medically attended, acute respiratory illness among nearly 140,000 people enrolled in a large managed care organization in Georgia.

Vaccine not fully protecting against respiratory illness

After adjusting for various factors, the Emory researchers observed that vaccine effectiveness for preventing serious respiratory illness was lower among patients taking statins, particularly when flu was widespread. They concluded that the effectiveness of flu vaccine in older people may be compromised by the use of statins.

Overall, statins appear to interfere with the response to influenza vaccine and lower the immune response, and this would also seem to result in a lower effectiveness of influenza vaccines.

The findings could have implications for guidelines for flu vaccine recommendations, statin use in older adults around the time of vaccination and future vaccine clinical trials in seniors.

Both teams call for additional studies, including research examining laboratory-confirmed cases of flu, to provide more guidance.

In a linked editorial, Drs. Robert L. Atmar and Wendy A. Keitel, of Baylor College of Medicine in Houston, TX, note that the findings should not yet affect how physicians care for their patients.

They comment:

"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."

The studies were financially supported by Novartis Vaccines, Emory University and the National Institute of Allergy and Infectious Diseases.

Medical News Today recently reported on progress toward a more effective flu vaccine that is able to respond to different strains of influenza.