A megadose of chicken pox vaccine
cuts the risk of shingles in adults aged 60 and older
— and reduces the severity of symptoms in those
who get it anyway, the FDA announced as it granted approval
for Merck's Zostavax on May 26.
While the sores of childhood chicken
pox may be a distant memory, the varicella zoster virus
that causes it lives on in spinal cells, ready to re-emerge
as herpes zoster, or shingles. Up to about 100,000 Canadians
a year fall prey, a number that's expected to increase
as the population ages. And the older the patient, the
more severe the pain and nerve damage tend to be. "We've
had patients who can't stand to put on clothes," says
Dr Carol Kauffman, chief of infectious disease at the
Veterans' Administration Ann Arbor Healthcare System.
Although patients generally respond well to treatment
with antiviral drugs, about 10-15% will be left with
painful post-herpetic neuralgia that can last months,
even years.
POX,
RELOADED
The vaccine was tested by a team of researchers from
Veterans' Administration (VA) in San Diego, led by infectious
disease expert Dr Michael N Oxman. The double-blind,
placebo-controlled study followed more than 38,000 patients
over the age of 60 for an average of three years, finding
that the vaccine cut the incidence of herpes zoster
by 51%. Where disease did occur, severity was reduced
by about 60% and the rate of post-herpetic neuralgia
was 66.5% lower in the vaccine group.
"If you're looking for good ideas
in medicine, you're lucky if half of them pan out,"
says Dr Oxman. "All of us were very gratified and pleasantly
surprised at the result of this trial." The results
appeared in the New England Journal of Medicine
on June 2, 2005.
MAKE
IT A DOUBLE
The doses of live, attenuated vaccine required are at
least 14 times higher than the minimum potency of Merck's
varicella virus vaccine, currently licensed to prevent
chicken pox in children. Dr Oxman says only those few
who never had chicken pox are likely to benefit from
the normal dose. The rest need the souped-up version
to reactivate their immunity to the zoster virus.
Despite its elevated potency, the
vaccine is well tolerated, with few serious adverse
reactions. Local reactions at the injection site, most
commonly erythema, pain or tenderness, or swelling,
were reported more frequently in the vaccine group.
The one caveat, says Dr Oxman, is that the vaccine shouldn't
be administered to anyone whose immune system is compromised,
or who's had shingles in the past.
A spokesperson for Merck Frosst
Canada Ltd told the Toronto Star the company
is working on getting Canadian approval for the vaccine,
but wouldn't speculate on when it'll happen. European
and Australian health authorities gave the go-ahead
earlier this month, Merck said. The vaccine — given
in a single injection — will sell for $152.50 US.
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