Did you know women may be more sensitive to some vaccines than men?

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Half-dose flu shots work in adults, study finds

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By LINDSEY TANNER, AP Medical Writer – Mon Dec 8, 4:44 pm ET

AFP/File – People fill out the paper work before getting their flu shots in 2006

in Chicago,

Illinois. Google is …

CHICAGO – 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. , 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, 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

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. 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. ph 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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