Higher-Dose Flu Shot Better for HIV-Positive People?
Flu shots work by essentially teaching the immune system to “recognize” flu viruses. These vaccines contain antigens, molecules on the surface of viruses and other microbes that allow the immune system to identify them as harmful invaders. If a vaccinated person is later exposed to the flu, the immune system produces molecules called antibodies that recognize those specific antigens and attack the virus, with the goal of preventing it from causing infection and illness.
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Researchers can anticipate how well a vaccine should work by checking antibody levels in the vaccinated individual’s blood; more antibodies should lead to better defense against the virus. That’s why a new study published in the January 1, 2013, issue of Annals of Internal Medicine is so intriguing.
Noah McKittrick of the University of Pennsylvania and colleagues compared antibody levels in HIV-positive study participants who received either a standard flu vaccine or the Fluzone High-Dose shot containing four times the usual dose of antigens, and found that those in the high-dose group produced significantly more of these protective antibodies.
Some important questions remain. The study did not examine whether the higher-dose flu shot produced any clinical benefit; that is, did people who received it actually avoid the flu more effectively than those who got the standard shot? The authors acknowledge this limitation, and note that assessing the clinical outcome of high-dose vaccination was beyond the scope of this relatively small study with 190 participants.
In addition, Fluzone High-Dose is currently approved for use only in people age 65 and older. Why have a separate flu shot just for older individuals? “Human immune defenses become weaker with age, which places older people at greater risk of severe illness from influenza,” states the Centers for Disease Control and Prevention’s fact sheet on Fluzone vaccines. “Also, [aging] decreases the body’s ability to have a good immune response after getting influenza vaccine. A higher dose of antigen in the vaccine is supposed to give older people a better immune response and therefore better protection against flu.” Might this rationale also support further exploring the use of Fluzone High-Dose in people whose immune systems are compromised by chronic HIV disease?
Although the study authors do not specifically address the issue of access to the high-dose vaccine, they do suggest that a new vaccination approach is warranted for people living with HIV. “The implications of this research are important for future vaccination efforts in the HIV-positive population,” the authors conclude. “This study suggests that a substantial number of HIV-infected patients may not be obtaining sufficient protection with the standard influenza vaccine.”
Reilly O’Neal is the editor of BETA.
Centers for Disease Control and Prevention. “Fluzone high-dose seasonal influenza vaccine: questions & answers.” Available at http://www.cdc.gov/flu/protect/vaccine/qa_fluzone.htm.
McKittrick, N. and others. Improved immunogenicity with high-dose seasonal influenza vaccine in HIV-infected persons: a single-center, parallel, randomized trial. Annals of Internal Medicine 158(1):19–26. January 1, 2013.