Second Chicken Pox Shot Boosts Coverage

Follow-up vaccination increases protection to nearly 100 percent.

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By Nathan Seppa, Science News

Two are better than one when it comes to chicken pox vaccinations, scientists report January 5 in The Journal of Infectious Diseases.

The chicken pox shot, first made available in the United States in 1995, has already proved able to prevent the disease in about 80 to 85 percent of children who get a single dose. In 2006, the Centers for Disease Control and Prevention and the American Academy of Pediatrics jointly recommended a two-shot approach, suggesting that children get the doses four to six years apart. The new study supports this revision: Adding another shot ups disease prevention to nearly 100 percent.

Pediatrician Eugene Shapiro of Yale University School of Medicine and his colleagues identified 71 children who had contracted chicken pox between 2006 and 2010, verifying the diagnoses with tests showing viral DNA in skin lesions on the kids. The children had attended 28 clinics in Connecticut. The researchers found that five of these 71 children hadn’t been vaccinated, and that 66 others had received a single shot.

But none had been vaccinated twice.

As a comparison group, the researchers identified 140 other children who matched the first group in age and had gone to the same clinics. None had come down with chicken pox. Of this group, 117 had gotten one shot, 22 had received two and one child hadn’t been vaccinated.

The authors calculate that the two-shot regimen was 98.3 percent effective in preventing chicken pox. Researchers at the Columbia University College of Physicians and Surgeons teamed with the Yale group.

The new study “is the first to evaluate the effectiveness of two doses of [chicken pox] vaccine in a real-world setting,” says physician David Kimberlin of the University of Alabama at Birmingham, who wasn’t part of the research team. “The effectiveness of the two-dose schedule is welcome news indeed,” he says, writing in the same JID issue.

Shapiro notes the recommended four- to six-year separation in the two doses is based on convenience, allowing doctors to give the second shot with other scheduled vaccinations. The second chicken pox vaccine shot can be given as soon as three months after the first dose, he says.

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