Stress may Lessen Flu Shot Effectiveness

The latest findings from a long-running project examining the effects of psychological stress on human health show that elderly caregivers are half as likely to see quick protection from flu shots as are other elderly people who aren't caregivers.

The study compared the immune responses of elderly men and women who cared for dementia patients with the responses of other elderly people not responsible for such care. The study was published earlier this month the Proceedings of the National Academy of Sciences.

These findings may have serious public health implications because they are the latest in a series of discoveries showing that people's immune systems can be seriously weakened by stressful events. Respiratory infections like pneumonia and influenza are a major cause of death among the elderly.

Blood samples were drawn just before the research subjects received influenza vaccinations this year. More samples were drawn 25 to 35 days after vaccination. A third sample was drawn from any of the elderly who hadn't responded to the vaccination within six weeks.

The researchers looked for a four-fold increase in the level of antibodies against the influenza virus as an indicator that the vaccine was working. They also measured levels of other immune system components -- Interleukin-1 and Interleukin-2 cytokine responses. And all subjects in the study underwent a screening to determine their levels of depression.

When they looked at the antibody levels, the researchers found that only 38 percent of the caregivers showed an adequate response while 66 percent of the controls produced the four-fold level of antibodies.

Caregivers showed lower levels of Interleukin-1 and Interleukin-2 in their blood, compared to the controls. Caregivers also showed "significantly higher levels of depressive symptoms than caregivers," the researchers wrote.

"Providing care for a spouse with dementia is remarkably stressful," explained Jan Kiecolt-Glaser, professor of psychiatry and psychology at Ohio State. "We've found in a variety of ways that the stress of caregiving appears to be associated with poor immune function."

"If we immunize a middle-aged population with the current vaccines, 80 percent to 90 percent of that group will be protected within a few weeks," biology department colleagueJohn Sheridan said.

"If I give the same vaccine to a group of people over age 65, then less than half of them will be protected by that first vaccination. If I give it to them for two to three years, the likelihood that they'll be protected increases dramatically."

Sheridan has tested the project's findings using laboratory mice and found similar results to those in the human studies.

The study's findings point to the importance of influenza vaccination, the researchers said.

"We're not saying that caregivers are at a greater risk of developing influenza," Sheridan said. "But if they have been vaccinated, they are likely to have less severe disease if they become infected.

"If you're a caregiver, it's important that you be vaccinated," he said, adding that getting the vaccine for successive years increases a person's resistance to the disease.

The research team is planning future studies at the newly created Institute for Behavioral Medicine Research at Ohio State to examine potential links between stress and other viral pathogens.