CHICAGO (AP) - Half-dose flu shots are effective in adults, especially in
women and those younger than 50, and offer a viable way to stretch supplies
during vaccine shortages, a government study found.
The strategy also might be an option during hard economic times since lower
doses likely would mean cheaper shots, said Vanderbilt University vaccine expert
Dr. Kathryn Edwards, who wasn't involved in the study. And the lower dosage
could open doors to vaccinating people in poor countries where flu shots are
little used, she said.
Even so, Edwards said giving half-dose flu shots isn't ready for prime time.
It's still experimental and hasn't been approved by federal authorities.
The study involved 1,114 adults aged 18 to 64. It's the first to test
half-dose flu shots in those aged 50 and older during a single flu season,
2004-05. The results among younger adults echo previous research, said lead
author Dr. Renata Engler of Walter Reed Army Medical Center.
The government-funded study appears in Monday's Archives of Internal
Medicine.
"Traditionally, vaccine programs have followed a 'one-size-fits-all'
approach," Engler said. That means everyone gets the same dose and during
shortages, supplies are more likely to run out.
If the study results are confirmed through additional research, Engler said,
half-doses could be given to large numbers of adults, enabling more people to
get vaccinated.
That's important because while influenza is often underestimated, the
federal Centers for Disease Control and Prevention says each year the disease is
responsible for about 36,000 deaths and 200,000 hospitalizations nationwide.
In the study, participants were randomly chosen to get full- or half-dose
flu shots in late 2004 in the Washington D.C. area. The researchers measured
blood levels of antibodies to flu virus before vaccination and 21 days
afterward.
After the shots, similar numbers of adults of all ages, including men and
women, had antibody levels considered adequate to protect against the flu.
The 18-to-49 age group and women had the highest antibody levels. That adds
to evidence that women may be more sensitive to some vaccines than men.
Dr. Ronald Hershow, an infectious disease specialist at the University of
Illinois's Chicago campus, noted that while half-doses produced an adequate
immune response, full doses produced a stronger response. And there's evidence
that stronger immune responses provide better protection against disease, he
said.
Still, the study authors argued that from a public health standpoint, it
would be better to vaccinate many people with lower doses than fewer people with
full doses when vaccine supplies are scarce.
There were few reports of flu-like illnesses among the study volunteers, but
the number of people of all ages with those symptoms was similar in both the
full-dose and half-dose groups.
Engler noted that because adults in their 60s and older are more vulnerable
to flu complications, more research is needed to be sure that half-doses are
adequate for them.
The study was done during the vaccine shortage in the winter of 2004-05 when
contamination was found at a major vaccine supplier's plant in Britain.
Now, there are five licensed flu vaccine manufacturers, making shortages in
the near future unlikely. Still, Dr. Joseph Bresee, the CDC's flu chief, said
the study provides useful information just in case.
Flu season starts in the fall and this year is off to a pretty typical
start, with low levels of disease nationwide, Bresee said.
"It's still a good time to get a vaccine," Bresee said,
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