Thaindian News

Washington, Jan 5 (IANS) Two doses of the chicken pox vaccine are more effective than one, researchers have found. The odds of developing the infection were lower in children who had received two doses of the vaccine compared with those who had received only one.

In a study, Eugene D.Shapiro, professor in pediatrics at Yale School of Medicine, and his team showed that the effectiveness of two doses was 98.3 percent.

The Centres for Disease Control and Prevention (CDC) recommended a single dose of chicken pox vaccine for children aged one to 13 years in 1995, the Journal of Infectious Diseases reports.

The chicken pox rate fell drastically and studies showed that the effectiveness of one dose was 86 percent. But there was still a high rate of breakthrough illness in immunised children, according to a Yale School statement.

The CDC changed the immunisation policy for chicken pox in 2006, adding a second dose for children aged between four and six years.

Past studies have suggested that two doses of varicella (chicken pox) vaccine are linked to higher antibody levels than one dose.

But this is the first study to assess the clinical effectiveness of two doses of the vaccine in the general population.

In a survey, Shapiro and his team discovered 71 cases of chicken pox in children aged four years and older.

None of these children had received two doses of vaccine, 66 (93 percent) had received one dose and five (seven percent) did not receive the vaccine.

“We weren’t surprised to find that two doses of varicella vaccine are highly effective and are more likely to prevent varicella than a singe dose,” Shapiro said.