Decision on Flu Vaccine: A Shot in the Dark?
It's Flu Season Again. To Vaccinate? Or Not to Vaccinate?
Despite the U.S. Health Service recommendation that adults with HIV infection receive annual influenza vaccine, concerns in the community persist. At a poster session at the Interscience Conference on Antimicrobial Agents and Chemotherapy, researchers from Detroit's Henry Ford Hospital presented data demonstrating that HIV-infected individuals experience a small, temporary increase in viral load after receiving the influenza vaccine.
Even in those whose HIV RNA was only detectable by an ultrasensitive assay (under 50 copies), an approximate three-fold increase was seen in about half the subjects. The significance of these transient increases remains unknown, but continues to fuel discussions among patients and providers every fall. A summary of the flu vaccine poster suggested that a genotypic evaluation of the elevated virus could yield valuable information about drug-resistant mutations that might occur.
Dr. Marshall Glesby and colleagues of Johns Hopkins University determined in a clinical trial in 1996 that "influenza vaccinations had no significant impact on average patient HIV levels" in adult patients with T-cells between 200 and 500.
Vaccines, which are weakened or inactivated forms of disease-causing agents, stimulate the production of memory cells, a type of immune cell. Exposure to weakened germ creates memory cells that are primed to quickly recognize the germ if it returns. The memory cells can then summon up the immune system's heavy weaponry to attack the infection before it spreads.
However, HIV infects and reproduces in a type of memory cell, the memory T-cell. "Scientists have been worried about giving a vaccine that causes memory T-cells to multiply," said Glesby. "That's because these cells act like virus factories when they're infected with HIV." Memory T-cells for any given germ are relatively rare, Glesby notes, and the number of those T-cells that are infected with HIV may be even more rare. This could explain the results of the study. "The vaccine may have increased production of a small group of memory T-cells, and because only a few of these memory T-cells were infected with HIV, the HIV RNA levels did not go up significantly."
But Dr. Glesby also cautioned that as T-cells decline, so does an HIV-positive individual's ability to mount an immune response to vaccination. "We should conduct further studies to determine if influenza is a common problem for HIV patients, and whether vaccinations are an effective way of reducing that problem," he said.
The viral load increase that occurs with flu infection itself may be more significant than that resulting from the vaccine and pose a greater threat of the outgrowth of drug resistant virus. Additionally, the frequent aftermath of flu (bacterial or viral pneumonia) can be far more perilous than the flu, particularly in an immunosuppressed individual.
In children, London researcher Dr. E.G.H. Lyall and colleagues report that flu shots only appear to be effective in the least symptomatic patients. Dr. Lyall's team evaluated the antibody response to flu vaccine in 25 HIV-infected children between the ages of 1 and 11. Most of the children had little or no detectable flu antibodies prior to vaccination.
Only 40 percent of the children developed new protective antibody responses. Those who did were the least symptomatic of the study subjects. The research team currently plans to vaccinate these children in the fall of 1997. They speculate that this may provide protection for other family members who may be even more immunosuppressed.
Where you work, the people you come into contact with, who you live with and a history of pneumonia or other respiratory problems all influence your personal risk associated with flu infection and the risk flu may pose to your overall health.
This article has been reprinted at The Body with the permission of AIDS Project Los Angeles (APLA).
This article was provided by AIDS Project Los Angeles. It is a part of the publication Positive Living.