Half-dose flu shots work in adults

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Half-dose flu shots work in adults, study finds

By Lindsey Tanner, Ap Medical Writer – Mon Dec 8, 4:44 pm ET

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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