September 2, 2008

Chickenpox Vaccine Does a Number on Number of Cases

By Liz Szabo

Cases of chickenpox -- a disease that was once nearly universal -- have fallen 57% to 90% in communities across the USA since a vaccine was introduced in 1995, a new report shows.

Before the vaccine, 4 million Americans a year came down with chickenpox, nearly 11,000 were hospitalized and more than 140 died, says a report from the Centers for Disease Control and Prevention in today's Pediatrics.

Hospitalizations have fallen 75% to 88%, and deaths in children ages 1 to 9 have declined about 90%, the study shows. Infections have even declined in babies too young to be vaccinated, who are being protected by "herd immunity" in which vaccines reduce infection in a community, says study author Jane Seward of the CDC's National Center for Immunization and Respiratory Diseases.

While the vaccine prevents 85% of general infections, it stops 95% of severe infections, which can lead to pneumonia and a brain inflammation called encephalitis.

Doctors encourage the vaccine because they can't tell which kids might develop pneumonia or encephalitis, says William Schaffner, a board member of the Infectious Diseases Society of America who was not involved in the study.

The CDC initially recommended one shot for toddlers ages 12 to 15 months. In 2006, the CDC suggested a booster shot for children ages 4 to 6. About 89% of children ages 19 to 35 months had received the shot by 2006, the study shows.

Doctors are learning more about the vaccine's safety, Schaffner says.

Kids who got a combined vaccine, protecting against chickenpox as well as measles, mumps and rubella, were twice as likely to develop fever and seizures, compared with those who got a chickenpox shot separately from the measles/mumps/rubella vaccine, the study shows.

About 5% of negative reactions to the vaccine have been serious, causing problems such as pneumonia and hepatitis, the study shows. Those problems occurred in patients with serious but previously undiagnosed medical conditions.

Doctors don't yet know how the vaccine will affect a community's natural immunity. Before the vaccine was introduced, people might be re-exposed to "wild" chickenpox many times throughout their lives, giving their immune systems the equivalent of a booster shot. Those boosts probably helped prevent shingles, Schaffner says. In shingles, the chickenpox virus hibernating in the body re-emerges, causing painful sores.

With less exposure to wild chickenpox viruses, Schaffner says, the immune system may not remain as strong, leaving people vulnerable to shingles.

In that case, Schaffner says, doctors may recommend the shingles vaccine be given to younger adults, such as 40-year-olds.


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