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Chickenpox Vaccine OKd; 70-to-90% Effectiveness Seen

March 18, 1995|MARLENE CIMONS | TIMES STAFF WRITER

WASHINGTON — The federal government Friday approved a long-awaited chickenpox vaccine, initiating an era when virtually all of the known major childhood diseases will be preventable.

The highly contagious disease, always a nuisance and sometimes life-threatening, afflicts nearly 4 million people annually, most of them children. Typically, it is a benign disease in children, but can be quite severe in teen-agers and adults or when unforeseen complications result.

"This vaccine has been studied in approximately 11,000 individuals and we expect it to be 70% to 90% effective in preventing chickenpox," Food and Drug Administration Commissioner David A. Kessler said in a statement.

The vaccine, which is manufactured by Merck & Co. Inc., of Whitehouse Station, N.J., is made from a live, but attenuated (weakened) form of the varicella virus--a member of the herpes family--which causes chickenpox.

The vaccine, which will be marketed under the trade name Varivax, will be available to pediatricians within eight weeks, the company said. It will cost $39 per dose, company officials said.

The company has recommended a single injection for children 12 months to 12 years of age, and two injections four to eight weeks apart in those age 13 and older, based on its studies of the vaccine in 9,454 children and 1,648 adolescents and adults. The vaccine is not recommended for those who have had chickenpox because they have lifelong immunity from the disease.

The federal Centers for Disease Control and Prevention is expected to issue official recommendations this spring on the timetable for including chickenpox in the childhood immunization schedule.

The FDA said the chickenpox vaccination can be administered at the same time as the combination shot for measles, mumps and rubella (German measles) without ill effects, meaning that both shots can be given during a single visit to the pediatrician.

The vaccine has been studied for more than a decade.

"This is a vaccine that is going to go potentially into every young child in the country--these are healthy kids and we wanted to make sure all questions were answered," said Kathryn C. Zoon, director of the FDA's center for biologics evaluation and research.

Among lingering concerns was the possibility of waning immunity over time, raising a potential that individuals immunized as children could become vulnerable to chickenpox later in life, when the disease can be far more serious.

Also, experts wanted to study the extent and severity of so-called "breakthrough" cases, which is when vaccinated patients contract the disease after exposure to naturally occurring chickenpox.

Also--as with natural chickenpox--the virus remains in the body's nerve cells for life, meaning that it could reactivate later as zoster (shingles), an especially painful skin condition, or as some other nervous system disorder. This could pose a special risk for patients with suppressed immune systems, or in anyone whose immunity to the virus has decreased.

But Dr. Philip Krause of the FDA's biologics center said that studies thus far have shown that these kinds of problems "are not likely to happen." The manufacturer will conduct strict post-market surveillance in coming years to ensure that any such problems are promptly identified, he said.

"It's easy to come up with theoretical concerns like that and they weigh heavily on us. But we are now confident, based on what we know about the vaccine, that those kinds of problems are very unlikely," he said.

"In the worst case scenario, if immunity wanes, these kinds of problems can be dealt with by requiring booster doses," Krause added.

On "breakthrough" cases, FDA and company officials said that the disease is far milder than in naturally occurring chickenpox. Breakthrough cases usually resulted in 50 or fewer lesions, compared to natural chickenpox, which typically causes 300 to 500 lesions, company officials said.

The vaccine has been endorsed by the American Academy of Pediatrics. "It is a very safe vaccine and it is going to be a very positive vaccine for kids," said Dr. Steve Kohl, a member of the academy's committee on infectious diseases. "I've been getting calls from pediatricians all the time asking: 'When is it coming?' "

Richard T. Perkins, founder and chairman of the VZV (Varicella-Zoster Virus) Research Foundation, which supports research and education on the virus, said: "We applaud the chickenpox vaccine as a breakthrough . . . and commend all who had a hand in its development."

Chickenpox, which is characterized by fever, weakness and a body rash that itches and blisters, had been virtually the only significant childhood ailment for which there was no vaccine available. Vaccines already are in widespread use for diphtheria, tetanus, pertussis (whooping cough), measles, mumps, rubella and polio, among others.

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