Some nonsteroidal anti-inflammatory drug (NSAID) painkillers may react with the immune system in a way that reduces the effectiveness of flu shots and other types of vaccines, a University of Rochester study finds.

The researchers said this is an important finding because an estimated 50 percent to 70 percent of Americans use NSAIDs for relief from pain and inflammation.

"For years, we have known that elderly people are poor responders to the influenza vaccine and vaccines in general," principal investigator Richard P. Phipps, a professor of environmental medicine and of microbiology and immunology, said in a prepared statement.

"And we also know that elderly people tend to be heavy users of inhibitors of cyclooxygenase such as Advil, aspirin, or Celebrex. This study could help explain the immune system response problem," Phipps said.

He and his colleagues conducted studies on mice and analyzed samples of blood from people who took part in early clinical trials of a new vaccine against human papillomavirus (HPV), which can cause cervical cancer.

They found that some NSAIDs hinder a vaccine's ability to prompt the immune system to produce antibodies against a specific illness/infection. The researchers said their findings suggest that it may be wise for people to avoid taking any NSAIDs when they receive any vaccine.

The study was published in the Dec. 1 online issue of the Journal of Immunology.