Painkillers may threaten power of vaccines

The findings are based on laboratory studies of blood samples from people who participated in early clinical trials for the HPV vaccine, and on studies of mice.

For the animal portion of the study, researchers vaccinated normal mice and mice engineered to be cox-2 deficient with a component form of the HPV vaccine. They analyzed the amount of antibodies the animals produced, focusing on the critical virus-neutralizing antibodies. The cox-2 deficient mice made 50 to 70 percent less of these key antibodies.

The same experiment was done on preserved blood samples from people who had been vaccinated against HPV-16, the strain linked to cervical cancer. Scientists reactivated the B cells in the blood samples and watched them churn out antibodies, as expected. But when researchers treated the B cells with a cox-2 inhibiting drug, the cells significantly diminished their production of antibodies – showing that cox-2 is essential for an optimal immune response against HPV 16.

This study is not questioning the effectiveness of the newly marketed HPV vaccine, the Rochester scientists said. They pointed out that in many clinical trials involving thousands of women, the vaccine offered complete protection against the development of cervical cancer. And presumably some of these women were taking NSAIDs at the time.

“There’s no doubt the HPV vaccine showed 100 percent efficacy. Still, our data does suggest that it might be wise to limit the use of NSAIDs when you receive any vaccine,” said co-author Robert Rose, Ph.D., associate professor of Medicine and Microbiology and Immunology at the University of Rochester, and one of the virologists whose work led to the development of the new cancer vaccine.

Scientists do not completely understand the mechanism by which cox-2 influences the immune response in humans. They do believe the response may depend upon the dose and frequency of NSAID use.

The negative effects of blocking cox-2 could be more pronounced in people with compromised immune systems, such as AIDS or cancer patients, the study noted. Moreover, if a vaccine is in short supply and needs to be given in lower-than-optimal doses, taking an NSAID could hamper the immune response even more.

In addition to Phipps and Rose, graduate student Elizabeth Ryan was a co-author on the study, with assistance from students Matt Bernard and Christine Malboef.