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Aspirin, Acetaminophen May Reduce Vaccine Effectiveness


Use of over-the-counter drugs such as aspirin, acetaminophen (Tylenol), and ibuprofen may reduce the effectiveness of vaccines for seasonal flu and H1N1, according to researchers at the University of Missouri-Columbia.

Drugs such as aspirin and acetaminophen work to relieve pain and fever by blocking the enzyme COX-1. Millions of people take aspirin daily for heart disease or pain management, and both acetaminophen and ibuprofen are also widely used for pain associated with headache, arthritis, and muscle aches.

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According to Charles Brown, associate professor of veterinary pathobiology in the Missouri University College of Veterinary Medicine, people who take these drugs regularly and then get a flu shot may not have a good antibody response. The reason, notes Dr. Brown, is that these drugs block COX-1, and “if you block COX-1, you might be decreasing the amount of antibodies your body is producing.” The body requires high levels of antibodies to protect against viruses.

Previous research revealed that other drugs that inhibit COX enzymes, such as the COX-2 inhibitors, have an effect on the effectiveness of vaccines. This new research by Dr. Brown’s team suggests that drugs that inhibit COX-1 may also have a negative impact on the ability of vaccines to perform. A recent study published in Lancet warned parents not to give acetaminophen to infants after they receive a vaccine because it reduces their immune response.

At this point, the research has only been tested in animal models, but the scientists will soon be applying it to people. If they find that aspirin, acetaminophen, and other COX-1 inhibitors affect vaccine effectiveness in humans, Dr. Brown notes that individuals may be advised to not take these drugs for several weeks before and after receiving a vaccine.

University of Missouri-Columbia news release, Dec. 1, 2009