Chicken pox vaccine effective over long term, Kaiser study finds

Once upon a time, not too terribly long ago, getting the chicken pox was practically a rite of passage for kids.

But now, nearly 20 years after approval of a vaccine for the varicella virus, which causes the itchy illness, chicken pox is a rarity. A new study conducted by researchers at Kaiser Permanente in Northern California and published online Monday in the journal Pediatrics confirms that the vaccine is, indeed, effective -- reducing cases of chicken pox in one large cohort of kids as much as tenfold over a 14-year study period.

For the study, the team monitored 7,585 children who received the varicella vaccine between June and November of 1995, at 12 to 23 months of age. Checking in every six months for 14 years, telephone interviewers asked caregivers if the immunized kids -- some of whom got second doses between 2006 and 2009 -- had developed chicken pox or shingles, which is also caused by the varicella virus. Parents also had a toll-free number they could call to report if their children fell ill.

Over the course of the entire study, parents reported just over 1,500 cases of “breakthrough” varicella in the immunized children, the equivalent of 15.9 cases per 1,000 person-years. If the kids had not been vaccinated, previous studies suggested, the rate would have been between 140 and 160 cases per 1,000 person-years. Additionally, very few of the illnesses were severe.

In the pre-vaccine era, the authors noted, most children had severe bouts, with more than 300 lesions on their bodies. Thousands were hospitalized, and around 100 people died, from the illness each year.

Among the vaccinated children, the team reported, the incidence of breakthrough cases declined over the course of the study, perhaps as a result of increased herd immunity, suggesting that the vaccine’s protection did not wane over time. None of the kids developed chicken pox after getting a second dose of the vaccine.

“Clearly, the vaccine is a very effective tool in preventing or limiting the severity of chicken pox in young people,” said pediatric infectious disease consultant Dr. Randy Bergen, of Kaiser Permanente’s Walnut Creek Medical Center, in a statement.

But Bergen added that keeping the disease at bay for large numbers of kids would depend on immunization rates remaining high. With parents in some places organizing “pox parties” or swapping infected candies with hopes of infecting their kids with the illness and providing immunity without having to give them a shot, that means public health personnel still face a steep challenge.

In 2011, Dr. Wilbert Mason, a professor of clinical pediatrics at USC’s Keck School of Medicine and an infectious disease expert at Children’s Hospital Los Angeles, told the Los Angeles Times that such strategies were extremely misguided, stressing that they place kids at increased risks for complications.

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