Aspirin, Tylenol may decrease effectiveness of vaccines, researchers say

With flu season in full swing and the threat of H1N1 looming, demand for vaccines is at an all-time high. However, researchers suggest that over-the-counter drugs may lessen their effect, ScienceDaily reported Dec. 2.

Although those vaccines are expected to be effective, University of Missouri researchers have found further evidence that some over-the-counter drugs, such as aspirin and Tylenol, that inhibit certain enzymes could affect the effectiveness of vaccines.

"If you're taking aspirin regularly, which many people do for cardiovascular treatment, or acetaminophen [Tylenol] for pain and fever and get a flu shot, there is a good chance that you won't have a good antibody response," said Charles Brown, associate professor of veterinary pathobiology in the MU College of Veterinary Medicine.

"These drugs block the enzyme COX-1, which works in tissues throughout the body. We have found that if you block COX-1, you might be decreasing the amount of antibodies your body is producing, and you need high amounts of antibodies to be protected."

COX enzymes play important roles in the regulation of the immune system. The role of these enzymes is not yet understood completely, and medications that inhibit them may have adverse side effects.

Recent research has discovered that drugs that inhibit COX enzymes, such as COX-2, have an impact on the effectiveness of vaccines. Brown's research indicates that inhibiting COX-1, which is present in tissues throughout the body, such as the brain or kidneys, could also affect vaccines' effectiveness.