Half-dose of flu shot effective

WASHINGTON, Dec. 9 (UPI) -- Adults under age 50 do not appear to have a different immune response to a half-dose of flu vaccine than to a full dose, U.S. researchers say.

The finding, published in the Archives of Internal Medicine, suggests that half-dose vaccinations of healthy young individuals may be effective in times of vaccine shortage.

Dr. Renata J.M. Engler of Walter Reed Army Medical Center in Washington and colleagues conducted a randomized clinical trial involving healthy adults ages 18-64. Between November and December 2004, 554 adults received a full dose of trivalent inactivated influenza vaccine and 556 received a half-dose of the vaccine.

All had been vaccinated within the past one to three years. Blood samples were taken before and 21 days after vaccination, and then tested for antibodies against influenza. Participants recorded any symptoms they experienced during this time period.

"Antibody responses to intramuscular half-dose trivalent inactivated influenza vaccine in healthy, previously immunized adults were not substantially inferior to the full-dose vaccine, particularly for ages 18-49 years," the study authors said in a statement. "Given the benefits of immunizing healthy working adults and caregivers, these data support the validity of a dose reduction strategy in the setting of vaccine shortages."