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Varicella vaccine exhibited long-term efficacy against illness
The varicella vaccine was effective in a 14-year study and appeared to reduce herpes zoster incidence as well, according to results of the study published online.
Roger Baxter, MD, of the Kaiser Permanente Vaccine Study Center, Oakland, Calif., and colleagues published data from a study that followed 7,585 children who were vaccinated with varicella vaccine in 1995. During the follow-up period, the incidence rate of varicella was nine to 10 times lower than corresponding rates in unvaccinated children of the same age in the pre-vaccine era, the researchers said. This resulted in an overall vaccine effectiveness rate of approximately 90%.
Roger Baxter
A total of 1,505 varicella breakthroughs were reported, but researchers said such cases decreased over time and no increase was observed during the 14 years of follow-up. The decline in breakthrough cases may have been caused by the second dose of vaccine recommendations instituted in 2006.
The risk for herpes zoster was not increased in vaccinated children and appeared to be lower in vaccinated children than in the pre-vaccine era, the researchers said.
“This study demonstrated the long-lasting effectiveness of the varicella vaccine. Because of herd immunity, effectiveness appeared to increase over time, instead of waning,” Baxter told Infectious Diseases in Children. “There was no shift of chicken pox into the older children and teens, and zoster appeared to be decreased compared with historical levels.”
Disclosure: Baxter reports receiving research grants from Merck.
Roger Baxter, MD, can be reached at the Kaiser Permanente Vaccine Study Center, 1 Kaiser Plaza, Oakland, CA 94612.
