VAIL, COLO. — The risk of herpes zoster in children under age 10 years who've been vaccinated against varicella was 4- to 12-fold less than in those with naturally acquired varicella in a large population-based study.
Moreover, when herpes zoster did occur, the pain was significantly less if the eruption was caused by the vaccine strain varicella zoster virus (VZV). This has previously been anecdotally reported, but the new study by the Los Angeles County Department of Public Health and the Centers for Disease Control and Prevention provides the first actual proof that herpes zoster in varicella vaccinees is a generally benign disease, Dr. Myron J. Levin said at a conference on pediatric infectious diseases sponsored by the Children's Hospital, Denver.
The study was conducted during 2000–2006 in Antelope Valley, Calif., a long-time CDC active surveillance site. During the study period, the incidence of herpes zoster among children less than 10 years old declined by 55%, from 74.8 cases per 100,000 in 2000 to 33.3 per 100,000 in 2006.
In contrast, the incidence jumped by 63% among 10- to 19-year-olds, from 59.5 to 96.7 cases per 100,000. The investigators said they couldn't explain this increase and would like to see it confirmed in other data sets in order to be confident the phenomenon is real (Pediatr. Infect. Dis. J. 2009;28:954–9).
One possible explanation for the increase over time in the older youths is waning VZV immunity, with resultant reactivation of the latent vaccine strain of the virus, according to Dr. Levin, professor of pediatrics and medicine at the University of Colorado at Denver.
Another possibility—and one he favors—is that the varicella vaccine is a suboptimal immunogen. Although the vaccine's primary failure rate is 4%–5%, as with other vaccines, the fact is that the boost in immunogenicity to varicella antigen following a first dose of the MMR vaccine is markedly less than the resultant immunogenicity boost to the measles, mumps, and rubella antigens. That's the basis for the two-dose strategy recommended by the CDC Advisory Committee on Immunization Practices in 2007.
The second vaccine dose boosts antibody to levels similar to those seen in adults after varicella. But boosted immunity will wane, and only time will tell how varicella vaccination will affect the incidence of herpes zoster. “We are in the midst of a very large clinical experiment,” Dr. Levin said of the two-dose strategy.
It makes sense that herpes zoster in VZV vaccine recipients should be less frequent and less severe than in naturally infected individuals because the vaccine virus is attenuated. Plus, the latent VZV that causes herpes zoster comes from skin lesions—and skin lesions are rare following vaccination of normal individuals. Dr. Levin disclosed that he is a consultant to, is on the speakers bureau for, and receives royalties from Merck & Co.
The incidence of herpes zoster among children less than 10 years old declined by 55%, from 2000 to 2006.
Source Dr. Levin