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Chicken Pox Shot Hits the Spot

Study shows steep declines in disease since U.S. vaccination program began

TUESDAY, Feb. 5, 2002 (HealthDayNews) -- For truth in advertising, look to vaccines.

Before the chicken pox inoculation was introduced in the United States in 1995, the disease annually infected 4 million people, mostly children, leading to 11,000 hospitalizations and 100 deaths.

But since the vaccine's arrival, the chicken pox case load has plummeted, a new study in tomorrow's Journal of the American Medical Association shows.

The researchers tracked chicken pox rates in three areas -- Antelope County, Calif., Travis County, Texas, and West Philadelphia, Penn. -- between 1995 and 2000. In all three regions, caseloads for the infection fell by as much as 84 percent after the vaccine appeared.

In Antelope County, the number of cases dropped from 2,934 to 837 during the period; in West Philadelphia, the case total went from 1,197 to 250; in Travis County, the decline was from 3,130 to 491.

In addition, hospitalizations due to chicken pox also fell markedly. Children between the ages of 1 and 4, the prime vaccination age, had the biggest drops in caseload, though the decline also occurred in older children and adults. Chicken pox, which is caused by the varicella-zoster virus, tended to surge in springtime.

By 2000, vaccine coverage for children ages 19 to 35 months ranged from 73.6 percent in Texas to almost 84 percent in Philadelphia County, which includes West Philadelphia, the researchers say.

Dr. Jane Seward, a CDC vaccine expert and the study's lead author, calls the results "a real success story."

If inoculations "sit on the shelf, they don't do anything to decline disease. With coverage reaching up to about 80 percent, disease goes down, as we would expect," she says.

Not only does the shot protect people of all ages, but it helps safeguard even those who don't get it by reducing transmission of the varicella virus in the entire population -- a phenomenon called herd immunity.

Seward says that's particularly important for children under a year old and those who have serious illnesses like leukemia that prevent them from getting immunized, she says. "The only way to protect them is to vaccinate those around them," she adds.

The government wants 90 percent of two-year-olds, and 95 percent of school-age children, to be vaccinated against chicken pox by the year 2010. Seward believes those marks will be met well before then.

The chicken pox vaccine schedule calls for a single shot for children between 12 months and 12 years old. But everyone over the age of 13, including adults, requires two injections, which are delivered four to eight weeks apart.

Seward says it's "critical" for everyone who can tolerate the vaccine to get it, because as childhood exposure falls, getting the infection as a teen or adult, when it's most serious, becomes more threatening.

The varicella vaccine initially faced resistance from both parents and physicians, who weren't sure its risks outweighed its reward. Dr. Barbara Yawn, director of research at Olmstead Medical Center in Rochester, Minn., and a chicken pox expert among the early skeptics, says the performance of the shot has solidified its acceptance in both camps. Most insurers now cover the injection, and as the rest follow suit coverage should continue to rise, she says.

Doctors are now concerned not about whether the vaccine works, but for how long. "Is this going to be lifelong immunity, or 20-year immunity, or will teens need a booster?" Yawn says.

Although the chicken pox vaccine is clearly effective, it's somewhat temperamental. A recent CDC study showed that protection against the virus weakens significantly if the immunization comes within 30 days of the shot for measles, mumps and rubella (the so-called MMR injection).

Even so, health officials say the overall risk of developing the disease for children who get the two injections too close together is still extremely low, and far smaller than if they were not vaccinated at all.

What To Do

To find out more about chicken pox, try the Centers for Disease Control and Prevention.

For more on the varicella vaccine, check out the University of Colorado or the Immunization Action Coalition.

SOURCES: Interviews with Jane F. Seward, M.B.B.S., M.P.H., acting branch chief, child vaccine preventable diseases branch, Centers for Disease Control and Prevention, Atlanta, and Barbara Yawn, M.D., M.S., director of research, Olmstead Medical Center, Rochester, Minn.; Feb. 6, 2002, Journal of the American Medical Association
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