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Vaccines can fail, but the reason may not be obvious

Determining why includes looking at the disease and the person as well as the immunization.

By Susan J. Landers, amednews staff. Jan. 28, 2002.

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Washington -- Vaccines are a wonder of modern medicine and have spared millions of people harm from such diseases as measles, polio, whooping cough and diphtheria.

However, sometimes vaccines fail to provide the reliable protection that many patients, especially the parents of young children, expect.

A recent outbreak of chicken pox in Connecticut, for example, resulted in a flurry of phone calls that kept Vincent Sacco, director of the state's immunization program, busy for several days.

He was able to tell parents that the number and severity of cases did not appear to be out of the normal range. He also stressed that his state is far from the 100% immunization rate that would make such an outbreak unusual.

Connecticut began requiring students entering preschool and kindergarten to be vaccinated against chicken pox in 2000, so many students are not yet immunized.

But outbreaks do occur, even among children already vaccinated.

"We don't always know the answer to why a vaccine fails," said Julia McMillan, MD, a professor of pediatrics at Johns Hopkins. "And chicken pox is probably the most problematic."

She was quick to note that the varicella vaccine is still a very good vaccine, with an effectiveness rate at about 85%.

And parents should be told that even if a child gets the chicken pox from a classmate or sibling after being immunized, the vaccine almost always protects them from "significant" infection, she said.

To really come to grips with why vaccines aren't 100% effective, "You have to look at the vaccine, the disease and the person," said Bruce Gellin, MD, executive director of the National Network for Immunization Information. [...]