Chicken pox flies coop thanks to vaccine

Chicken pox has flown the coop for many youngsters thanks largely to the varicella vaccine, a recent Kaiser Permanente Vaccine Study Center report contends.

Kaiser researchers tracked the progress of 7,585 children who received the vaccination in 1995 — when it was initially licensed and endorsed for use by the Advisory Committee on Immunization Practices. Over the course of a 14-year study period, the researchers observed the long-term capabilities and effectiveness that the treatment had on both varicella and herpes zoster, or shingles.

According to the findings, the children involved in the study (who had all received the vaccine) were 9-10 times less likely to contract varicella, marking the shot’s effectiveness at nearly 90 percent.

"Clearly, the vaccine is a very effective tool in preventing or limiting the severity of chicken pox in young people," said Randy Bergen, MD, chief of outpatient pediatrics at Kaiser Permanente's Walnut Creek Medical Center and a pediatric infectious disease consultant, in a news release. "As with any vaccine, though, the rate of vaccination has a huge impact on effectiveness. The more children vaccinated, the more effective the vaccine is for the entire community. At Kaiser Permanente, our use of a comprehensive electronic health record, KP HealthConnect, enables us to quickly identify children in the targeted age ranges who have not been vaccinated, and to reach out to their parents to ensure they get the shots. Keeping vaccination rates high confers benefit on the community as a whole because there are fewer children who can contract and spread the virus."

Overall, 1,505 breakthrough cases of varicella were recorded within the study pool. Such instances were characterized as follows: mild — less than 50 lesions; moderate — 51 to 300 lesions; and severe — more than 300 lesions. Only 28 children were said to have come down with severe chicken pox despite having been vaccinated. The study team concurred that before the vaccination epoch, most children were faced with symptoms of elevated severity. These breakthrough cases were also noted to have decreased over time, leading to an effectiveness increase “likely the result of vaccine failure occurring early, while breakthroughs became rare due to high vaccine effectiveness both directly and through herd immunity," explained Roger Baxter, MD, co-director of the Kaiser Permanente Vaccine Study Center, in a prepared statement.

Following the second dose of varicella vaccine given in 2006 to the children, then aged 4-6, breakthrough case decline continued steadily throughout 2008 and 2009. Scientists were quick to assert, though, that second dosage may be of even more benefit if given closer to the first dose, especially if varicella is in season.

Happenstances of herpes zoster also showed no increase in vaccinated children, with only 46 confirmed cases reported among the participant pool (a 40 percent decrease). Such study outcomes, partnered with the chicken pox facts, can be referred to by physicians when discussing with patient parents the benefits of vaccination.

The study can be found here in the latest edition of the journal Pediatrics.