Chicken Pox Vaccine Exceeds Expectations

Hospitalizations, costs, adult illness down since debut a decade ago

TUESDAY, Sept. 7, 2004 (HealthDayNews) -- The chicken pox vaccine has performed more effectively in its first decade than researchers had predicted, a new study says, saving money and preventing illness even in adults who have not had the shot.

Since more children have become vaccinated, thousands have been spared hospitalization for severe disease and society is saving $100 million each year in hospital bills alone, according to Dr. Matthew M. Davis, the study's lead author and an assistant professor of pediatrics, internal medicine and public policy at the University of Michigan Medical School.

"We were surprised at the magnitude of the savings," Davis said. "The general prediction before the vaccine was licensed was that there would be about $70 to $80 million saved [annually] in hospitalizations."

The study appears in the September issue of Pediatrics.

The savings reflect only hospitalizations, not doctor visit costs, medication or lost work time.

Chicken pox, caused by the varicella zoster virus, is one of the most common childhood diseases, according to the American Academy of Pediatrics. Until the late 1990s, there were about 4 million cases a year, with 11,000 hospitalizations and 100 deaths, according to the U.S. Centers for Disease Control and Prevention.

The rate of hospital discharges for chicken pox dropped 74 percent in the first six years after the vaccine went on the market in 1995, the authors reported. Before the vaccine was introduced, one chicken pox-related hospitalization occurred each year for every 20,000 Americans. By 2001, the rate was 0.26 hospitalizations for every 20,000 people.

One dose of the vaccine is recommended for children between ages 12 and 18 months. Those who don't get the vaccine until they are 13 years or older should get two doses, four to eight weeks apart, pediatricians recommend.

While previous research found no significant difference in the rates of chicken pox-related hospitalizations, those studies had smaller sample sizes, the authors noted, or required the researchers to pool information from multiple years, losing the chance to examine year-to-year trends.

For the new study, researchers analyzed data from a nationally representative annual sample of discharges from non-federal, short-term, general and children's hospitals. They calculated vaccination rates using information from the CDC's National Immunization Survey.

The savings are even more impressive, Davis said, when one considers that the national chicken pox immunization rate for 19- to 35-month olds in 2001 was 76 percent, not the 90 percent projected for that time.

Although the chicken pox vaccine program principally targets kids in their toddler years, Davis said, "we saw benefits from the vaccine among older kids as well as adults. That effect is traditionally known as 'herd immunity,' where those not vaccinated reap the benefits of others being vaccinated [because there is less overall exposure]."

But he cautioned parents not to rely on that phenomenon as a reason not to vaccine their children.

"Everything they say is accurate," said Dr. Cody Meissner, chief of pediatrics at Tufts-New England Medial Center in Boston. "The vaccine has had an enormous impact on the disease."

He, too, cautions parents not to rely on herd immunity. "If a child is not vaccinated, he or she will come down with chicken pox if they come into contact with an adult who has shingles," he said, referring to a painful adult condition that is caused by the same virus. An unvaccinated child may not get chicken pox until he or she is older, and the disease can be much more severe in adults, added Meissner, who is vice chairman of the American Academy of Pediatrics' committee on infectious disease.

More information

To learn more about chicken pox, visit the American Academy of Pediatrics.

SOURCES: Matthew M. Davis, M.D., assistant professor, pediatrics, internal medicine, and public policy, University of Michigan Medical School, Ann Arbor; Cody Meissner, M.D., vice chairman, committee on infectious disease, American Academy of Pediatrics, and chief, pediatrics, Tufts-New England Medical Center, Boston; September 2004 Pediatrics
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