Taking cholesterol-lowering statins may help fight heart disease and stroke in older Americans, but the drug’s cardiovascular benefits might come at a very viral cost. Two new studies revealed that the popular meds may also interfere with the efficacy of annual flu vaccines, NBC News reports.

For the first study, researchers at the Cincinnati Children’s Hospital looked at data from 7,000 people older than 65 who got flu shots over a nine-year period. Scientists found that patients who took statins produced fewer flu-fighting antibodies after getting their vaccines than those who didn’t.

In the second study, researchers at Emory University in Georgia checked the cases of nearly 140,000 older patients in a managed care program. Similarly, they found those who took cholesterol-lowering drugs received less protection from severe respiratory disease than those who didn’t take these meds after getting their annual flu shots.

Researchers said the new findings might help explain why flu vaccines tend to work so poorly among older people when compared with the rest of the population. But scientists from both studies also stressed that it’s far too soon to assume statins are directly and entirely to blame for the disparity.

“There are several other reasons, one of them being that our immune system becomes somewhat less effective as we age,” said Saad Omer, MD, of Emory University, the leader of the Emory research team.

In the meantime, doctors are suggesting folks older than 65 get new high-dose flu vaccines that seem to boost the immune response of many in this population group.

Studies also show women may get a bigger immune boost from flu shots than men. For more information, click here.