Stress can have all sorts of negative health effectsweight gain, sleeplessness, high blood pressure, to name a few. Now it appears stress can even diminish the efficacy of vaccinations. According to a report published in this month's issue of the journal Psychosomatic Medicine, stressed vaccine recipients developed a considerabley weaker immune response than did vaccine recipients who were not under stress. Earlier work had shown that a patient's stress levels can affect a viral vaccine's potency, but the new results show that the same holds true for bacterial vaccines, such as those that protect against pneumonia.

Ohio State University researcher Ron Glaser and his colleagues studied 52 older adults who had never before received a pneumonia vaccine. They divided the subjects into three groups. One consisted of those who were caring for spouses suffering from dementia (a situation known to cause chronic stress), another contained former caregivers, and the rest formed the control group. Initially, participants in all three groups showed a positive response to the vaccine, including high levels of immunoglobin-G (IgG), an antibody the body produces to fight pneumococcal bacteria. But several months later, blood samples from the current caregivers revealed a considerably weaker immune status. Participants belonging to the other two groups, in contrast, maintained their vaccine-enhanced immunity.

Exactly what accounts for the pattern of an initial response and subsequent decline in the stressed caregivers remains unclear. (In a similar study of the viral influenza vaccine, caregivers and former caregivers both exhibited a weaker immune status than did the control group almost immediately after innoculation.) But Glaser notes that elderly Americans planning their annual pneumonia and flu vaccinations should heed these results and consider rescheduling the shots if they are highly stressed. "The bottom line is that they should probably wait until they feel less stressed," he says. "If they do, they may stand a better chance of developing a stronger immune response from the vaccine and therefore better protection against the disease."