After receiving the flu vaccine, people sometimes experience achy muscles, fever, headaches, and pain at the injection site. To avoid that discomfort, some might take acetaminophen (Tylenol) or nonsteroidal anti-inflammatory drugs (NSAIDs) before getting their vaccine. Yet few studies have examined if taking analgesics before receiving a flu shot might affect one’s immune response or the shot’s effectiveness. 

A study published late last week in the Journal of Infectious Diseases found that taking NSAIDs or acetaminophen in the 24 hours before receiving a flu shot did not reduce the vaccine’s effectiveness or change people’s immune response. Common over-the-counter NSAIDs include ibuprofen (Advil, Motrin) and naproxen sodium (Aleve).

“There is no evidence that [pre-vaccination] analgesic use is associated with reduced influenza vaccine immunogenicity or effectiveness,” wrote the US Department of Defense researchers who conducted the randomized clinical trial. 

The research included US military personnel enrolled in the Pragmatic Assessment of Influenza Vaccine Effectiveness in the DoD (PAIVED) trial for one of two studies to examine how taking NSAIDs or acetaminophen prior to vaccination affected their immune response and the vaccine’s effectiveness. 

In one study, scientists looked at 684 participants—with 10.4% (71) using NSAIDs or acetaminophen—to understand how analgesics use prior to vaccination impacted immunogenicity. Participants agreed to bloodwork one month before and after vaccination to allow researchers to examine immune response. Also, they participated in weekly surveys about flu-like symptoms. Those reporting symptoms visited the clinic or participated in a virtual clinic and had nasal swabs taken. The researchers found no association between using analgesics and immunogenicity. 

There is no evidence that [pre-vaccination] analgesic use is associated with reduced influenza vaccine immunogenicity or effectiveness.

To determine the role of analgesics on vaccine effectiveness, the researchers examined 10,723 participants, with 10.6% (1,140) of the group taking analgesics. They also participated in the surveys about symptoms and flu-like illnesses and visited a clinic if they experienced such symptoms. The researchers detected no association between taking NSAIDS or acetaminophen and the risk of developing flu. 

“The primary finding that analgesic use within the day prior to vaccination has minimal to no effect on vaccine-induced antibody response is consistent with the limited literature on [pre-vaccination] analgesic use in adults, which has largely focused on COVID-19 vaccination,” the authors wrote.