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Statins May Decrease Efficacy of the Flu Shot

The anti-inflammatory effects may interfere with immune responses.

Statins are commonly prescribed drugs used in cardiovascular disease because they lower serum cholesterol. The drugs also have anti-inflammatory effects. For example, they inhibit leukocyte chemotaxis, proinflammatory cytokine propagation, and antigen presentation, among other alterations in the inflammatory response pathway. A study published in the Journal of Infectious Disease suggests that this property appears to interfere with the body’s immune response to the influenza vaccine.

The authors conducted a retrospective cohort study of existing patient data from Kaiser Permanente in Georgia. For nine flu seasons between 2002-2003 to 2010-2011, the authors identified patients who received vaccination, and noted any incidences of medically attended acute respiratory illness (MAARI), which is often a surrogate marker of influenza vaccine efficacy. They also noted statin use. Patients had to be at least 45 years old on September 1st of the flu season, and not be pregnant or receiving immunomodulating medications or therapy. Patients with cancer, transplantation histories, or HIV/AIDS infection were also excluded.

The authors found that influenza vaccine effectiveness decreased among patients taking statins. During local influenza activity, vaccine effectiveness against MAARI for statin users was lower than for nonusers (14.1% vs. 22.9%, 95% CI -1.7% to 26.1%). Vaccine efficacy among statin users was decreased during periods of widespread influenza activity as well (12.6% vs 26.2%, 95% CI, 2.9%-36.2%). This reduction in effectiveness appears to be more prevalent among male than female users.

It is important to note that MAARI can be caused by other infections, not just the influenza virus. Therefore this study should be repeated, but with clinical confirmation of influenza infection being the primary endpoint instead of MAARI.

It is also important to note that, despite possible reduced efficacy among statin users, the influenza vaccine should still be given to most people. The decrease in vaccine efficacy is not a contraindication.

Practice Pearls:

  • A retrospective cohort study suggests that statin use may decrease the efficacy of the influenza vaccine.
  • The decrease in efficacy affected males more than females.
  • Vaccine effectiveness was measured via MAARI, not rates of clinical influenza infection, so the study needs to be repeated with confirmed influenza infection as an endpoint.

Omer SB, Phadke VK, Bednarczyk RA, et al. Impact of Statins on Influenza Vaccine Effectiveness Against Medically Attended Acute Respiratory Illness. J Infect Dis. (2015). First published online: October 28, 2015. doi: 10.1093/infdis/jiv457