Chickenpox Vaccine Cuts Contagiousness

Vaccinated Youth Spread the Disease Less

From the WebMD Archives

Aug. 10, 2004 -- New research shows that the chickenpox vaccine not only helps those who get it but also those around them.

Children and teens who have taken the chickenpox vaccine are nearly half as contagious as unvaccinated people, according to a new study.

Chickenpox is caused by the varicella zoster virus and is spread by droplet or airborne transmission. It mainly affects children and is marked by the sudden onset of a rash with no other known cause. Most people get chickenpox once.

Some people who have received the chickenpox vaccine still get the disease. Typically, they have milder symptoms and fewer skin lesions than unvaccinated people. In addition, they are often less contagious, according to research led by Jane Seward, MBBS, MPH, of the CDC.

Seward and her colleagues examined reports of chickenpox cases in a community of nearly 320,000 people in Los Angeles County, Calif., between 1997 and 2001. Cases were reported by a wide variety of sources including schools, child care centers, doctors, hospitals, homeless shelters, and companies with more than 500 employees.

The data detailed the age, chickenpox history, and vaccination record of everyone in households affected by chickenpox.

A total of 6,316 cases were reported during the study. Overall, patients who had received the chickenpox vaccine were half as contagious as unvaccinated persons with chickenpox, writes Seward.

The number of skin lesions was connected to the level of contagiousness among vaccinated patients. Those with fewer than 50 lesions were only one-third as contagious as unvaccinated people, while those with 50 or more lesions were just as contagious as unvaccinated people.

The study also showed the protective power of the chickenpox vaccine among children aged 1 to 14 years old. Of those exposed to unvaccinated people, 72% contracted chickenpox if they were unvaccinated, while only 15% got it if they had been vaccinated.

The chickenpox vaccine is routinely given to children in the U.S. who are at least 12 months old. Before its development and widespread use, there were about 4 million chickenpox cases in the U.S. each year, causing 10,600 hospitalizations and 100 deaths.

The study appears in the Aug. 11 issue of TheJournal of the American Medical Association.

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SOURCES: Seward, J.F. The Journal of the American Medical Association, Aug. 11, 2004: vol 292; pp 704-708. News Release, The Journal of the American Medical Association.
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