Published online October 1, 2004
PEDIATRICS
Vol. 114
No. 4
October 2004, pp.
1130-1131
(doi:10.1542/peds.2004-1110)
Chickenpox Outbreak in a Highly Vaccinated School Population
Karl Heath, RN
Barbara Watson, MD, FAAP
Division of Disease Control
Philadelphia Department of Public Health
Philadelphia, PA 19146
To the Editor.—
A recent Pediatrics article on varicella outbreak in Oregon1 reported that >5 years since vaccination was associated with a significant increase in the risk of breakthrough disease. The co-index subjects were all unvaccinated, and the secondary subjects were vaccinated. Although vaccinated subjects are infectious, they are less infectious than unvaccinated subjects in household settings (Varicella Active Surveillance Project, unpublished data, 2003). Therefore, students exposed to the co-index unvaccinated subjects have a more intense exposure than later subjects who were mainly exposed to children with breakthrough disease. If the co-index subjects were older (and it is likely that they were, because school immunization requirements have been implemented gradually, leaving older grades with more remaining susceptibles), then the classmates exposed to the unvaccinated co-index subjects were also older. These older children are more likely to have a longer time since vaccination.
Without knowing the age of those exposed to unvaccinated subjects (ie, cases occurring after the first incubation period) as compared with the ages of those exposed to vaccinated subjects (ie, cases occurring in subsequent incubation periods), it is not possible to determine if the length of time from vaccination among subjects with breakthrough disease is a reflection of greater exposure to older unvaccinated subjects. It would be worthwhile to account for this difference in exposure. It might be possible to stratify by generation of subjects, because the first generation of subjects was exposed to highly infectious unvaccinated subjects; whereas the following generations were exposed to less-infectious breakthrough subjects. We suspect that the first generation would be older than the second generation of subjects, which might partially explain the difference in time since vaccination.
REFERENCE
- Tugwell BD, Lee LE, Gillette H, Lorber EM, Hedberg K, Cieslak PR. Chickenpox outbreak in a highly vaccinated school population.
Pediatrics. 2004;113
:455
–459[Abstract/Free Full Text]
PEDIATRICS (ISSN 1098-4275). ©2004 by the American Academy of Pediatrics
