Flu shot half dose just as good for younger adults
By Will Dunham
WASHINGTON (Reuters) - A half dose of flu vaccine may work just as well as the full dose for healthy adults under 50 — a finding that could help stretch supplies in the event of a future vaccine shortage, researchers said on Monday.
The study involved about 1,100 U.S. adults, about half of whom were given a half dose of influenza vaccine in November and December 2004 and the rest were given a full dose.
Blood samples given three weeks after vaccination showed that the immune systems in those ages 18 to 49 were stimulated at similar levels whether they got a half or full dose. And both groups got flu symptoms at similar rates, the researchers wrote in the journal Archives of Internal Medicine.
The people in the study, primarily current and retired U.S. military personnel, received flu shots and not the nasal spray vaccine. All of them also had received a flu shot within the prior one to three years.
Dr. Renata Engler, a U.S. Army colonel and an immunologist at the Walter Reed Army Medical Center in Washington, said the study also showed that guidelines for vaccine use during shortages should take a person’s sex into consideration.
“The immune response of women — actually regardless of age group — was significantly higher than the immune response of males,” regardless of the dose they received, Engler, who led the study, said in a telephone interview.
Dr. Andrew Pavia of the University of Utah Health Sciences Center, who heads a pandemic flu task force for the Infectious Diseases Society of America, said the findings could be important in the event authorities need to extend vaccine supplies due to limited supplies of flu vaccine or the emergence of a human pandemic caused by bird flu.
“I think it’s one more strategy we could turn to in the face of a critical shortage,” Pavia, who was not involved in the study, said in a telephone interview.
U.S. health authorities said there currently are ample supplies of flu vaccine. The U.S. Centers for Disease Control and Prevention this year expanded by 30 million the number of children who should get the flu vaccine.
CDC officials said 261 million Americans — 85 percent of the population — should be vaccinated for an influenza season that is expected to peak in January and February.
Flu viruses constantly mutate, forcing health authorities to update the vaccine annually to try to counter the strains predicted to be circulating in the population.
Companies that make flu vaccine for the U.S. market include Sanofi Pasteur, Australia’s CSL Ltd, GlaxoSmithKline Plc, Novartis AG and nasal spray maker MedImmune, acquired by AstraZeneca Plc.
Flu kills about 36,000 people and sends 200,000 to the hospital in the United States annually. A pandemic of a new type of influenza could kill many more and experts are working to improve flu vaccine production and distribution.
(Editing by Philip Barbara)
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