Dr. Sandra L. Snow and colleagues from the Arkansas Department of Health conducted a study during an outbreak of chicken pox at one of the schools. They observed that 96% of the 545 children attending the school had not suffered chicken and had taken the vaccination, and 14 among them had been given 2 doses of the vaccine.
It was found that 43 of the 48 students who developed chickenpox had received the vaccines and the most vulnerable classroom for maximum chicken pox spread was the first grade classroom, where all pupils had received the vaccine. It was noted that, those vaccinated had the disease in a milder form and did not have to miss school for more than 2 days.
According to the report, the vaccine had an 82 percent efficacy for any type of chickenpox, and 97 percent for moderate or severe cases. The investigators concluded that a single dose of varicella vaccine is insufficient to offer the required immunity to guard against the outbreaks in schools. In their estimate, a two-dose vaccine administration would be effective in offsetting an outbreak, compared to just a single dose.