Statins are powerful, unusual, and, like El Niño and Tom Cruise, not well understood. Statins have a huge upside. They improve survival after heart attacks and lower the risk of recurrent strokes. They are also the only cholesterol-lowering medications that have been clearly shown to reduce heart attacks and deaths in high-risk patients without heart disease. In addition to reducing cholesterol, statins also lower levels of inflammation in the body. Reducing inflammation probably helps statins to prevent heart attack and stroke. However, evidence is emerging that these statin effects may also have a downside, hindering the ability of the immune system to fight infections.
Teasing out the relationship between statins and immune response
Two recent studies examined the relationship between statins and the immune response to the influenza vaccine. For the first study, researchers at Emory University looked at a large database of patients in a managed care organization to see if there was a connection between statin use, flu vaccination, and the frequency of doctor visits for flu-like illnesses. They found that patients who received the flu vaccine were more likely to seek treatment for a respiratory illness during flu season if they were also taking a statin, compared with patients who had received the flu vaccine but were not taking statins. This suggests that patients on statins may not have responded as well to the flu vaccine as those who didn’t take the cholesterol-lowering drug.
The other study provided concrete evidence of the weaker immune response to the flu vaccine in people taking statins. For this study, researchers looked at data from over 5,000 patients enrolled in a clinical trial of a new flu vaccine. They found that levels of antibodies directed against the influenza virus were lower in patients taking statins, compared with patients who were not taking statins.
Both of these studies had one major limitation. Patients taking statins were more likely to have serious underlying diseases, such as diabetes, heart disease, COPD, neurologic disorders, or kidney disease, compared with patients not taking statins. So the poor response to flu vaccine and the apparent greater risk of flu-like illness in patients on statins could have been the result of their high burden of chronic disease, and not their statin therapy. Of note, one randomized trial in healthy young volunteers showed no effect of statin therapy on antibody responses to the hepatitis A vaccine.
There is also a bewildering variety of other research about statins and their effects on the human immune response. At various points, statins have been associated with each of the following: a lower risk of dying from influenza; a lower risk of dying from influenza in some years, but not others; a slightly increased risk of shingles (herpes zoster); a lower risk of pneumonia; neutral effects on pneumonia risk; and a lower risk of dying from pneumonia.
But don’t quit your statin just yet…
Based on current evidence, I don’t think we need to change how we prescribe statins, which are tremendously beneficial drugs, but we do need more information about how statins influence the risk of infection. Patients taking statins may want to consider getting the high-dose influenza vaccine, which results in higher antibody levels and greater protection against the flu, compared to standard-dose vaccine.