Flu shots may backfire on people with AIDS, raising the level of the AIDS virus in their blood without protecting them from the flu, a new study has found.
Researchers at the University of California's San Francisco Medical Center found that most study participants had three times the normal amount of HIV in their blood for a short time after getting an influenza vaccination.
The flu vaccine activates the same immune-system cells that harbor HIV, causing it to multiply as the cells divide, according to the researchers, who presented the study this week at the annual meeting of the American College of Allergy and Immunology in San Francisco.
Blood levels of HIV, known as the viral load, are thought to help predict the outcome of AIDS. But the impact of a short-term elevation of the AIDS virus is not known, said Dr. Howard Grossman, a New York City doctor with a large HIV practice.
Some researchers point out that developing the flu may be worse for people with weakened immune systems than getting the vaccine.
"We can't interpret this data to modify our vaccine use," said Dr. Bruce Walker, an AIDS immunologist of Harvard University. "We don't know what happens when a person gets infected with the flu. The infection may cause an even higher viral load."
The Centers for Disease Control and Prevention in Atlanta now recommends that all people with weakened immune systems, including those infected with HIV, get annual flu shots, and the agency has no plans to change its advice.
"Influenza and pneumococcal infections are major killers, especially of people at risk, such as those with HIV infection," said CDC health education specialist Barbara Reynolds.
The new study found that 78 percent of HIV-positive people given flu shots had an increase in their blood levels of HIV, but only 44 percent made antibodies to influenza as a result of the shot. In a comparison group of people not infected with the AIDS virus, 100 percent developed flu antibodies after receiving a flu vaccination.
The California study may lead to improved methods of vaccination, said Dr. James Kahn, who also works at the UCSF Medical Center.
"Perhaps patients should be taking anti-AIDS drugs such as AZT when getting vaccinations, to block the increase in viral load," Dr. Kahn said.