By Suzanne Rostler

NEW YORK, Mar 28 (Reuters Health) - The days of "chickenpox playgroups" may have gone the way of pine-paneled station wagons and wall-to-wall shag, replaced by a simple shot in the arm, study findings suggest.

The chickenpox vaccine became available in the US in 1995 and is now recommended by the American Academy of Pediatrics (AAP) for healthy children 12 months and older who have not had chickenpox. Dr. Marietta Vazquez of Yale University in New Haven, Connecticut, and her colleagues are conducting an ongoing trial of the vaccine.

The vaccine is safe and is 97% effective in protecting children aged 12 months to 16 years from contracting a severe form of the disease. While 86% of the 56 vaccinated children in the study who developed chickenpox had a mild form of the disease, only 48% of the 187 unvaccinated children with chickenpox did, the researchers report in the March 29th issue of The New England Journal of Medicine.

Chickenpox can lead to more serious complications in adults. For this reason, generations of parents have knowingly exposed their children to other kids with the virus, since an estimated 90% of unvaccinated people will catch the disease when exposed to an infected person.

But while many children contract and recover from chickenpox through these gatherings, known as chickenpox playgroups, others have experienced serious complications including encephalitis (inflammation of the brain), pneumonia and death.

According to the AAP, about 4 million cases of chickenpox occurred in the US each year before the introduction of the varicella vaccine, resulting in 10,000 hospitalizations and 100 deaths.

Further, chickenpox is occurring among younger children, who are more susceptible to group A streptococcus bacterial infections. These bacteria cause mostly mild infections such as strep throat, but in rare instances can lead to more serious infections including necrotizing fasciitis and streptococcal toxic shock syndrome.

"These results indicate that the effectiveness of the varicella vaccine as it is used in actual practice is excellent, at least in the short term," Vazquez and colleagues write.

How long immunity from one shot will last, they note, remains unclear.

Previous studies have shown that the vaccine used in the current study can cause mild side effects such as rash, fever, sore throats and cold-like symptoms, and that the rate of more serious side effects is extremely rare. The current report did not investigate side effects.

Last year, the US Centers for Disease Control and Prevention recommended that children be vaccinated against the chickenpox virus before entry to childcare facilities and elementary schools.

"It is important for all susceptible persons, adults as well as children, to get vaccinated against varicella," Vazquez stressed in an interview. Immunizing children "not only provides them with protection against the disease but prevents them from becoming susceptible adults."

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