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BACKGROUND: Outbreaks of varicella in New York City (NYC) schools declined substantially since a routine second dose of varicella vaccine was recommended in 2006. In NYC, two doses of varicella vaccine are required for entry into kindergarten and grade 6 as part of a rolling requirement, and one dose of varicella vaccine or other evidence of immunity is required for all other grades. We describe a varicella outbreak investigation in a NYC public elementary school.
METHODS: Varicella cases were reported by the school to the NYC Department of Health and Mental Hygiene (DOHMH). Investigation of suspected cases included patient interview and medical and immunization record review. Polymerase Chain Reaction (PCR) with genotyping and varicella IgM testing were performed. Students with generalized maculopapulovesicular rash and/or varicella diagnosis by a provider, or epidemiologic linkage to a case were classified as confirmed.
RESULTS: Sixteen cases were confirmed with onset dates from October 21 to November 21, 2014. Among the cases, 13 were attendees of the school (student-population= 659) and 3 were relatives of students. Cases in the school occurred in all grades from pre-kindergarten through grade 5. Cases ranged in age from 2 to 47 years, with a median age of 6 years. Symptoms were generally mild to moderate with 13 (81%) cases having <250 lesions. Among all 16 cases, 9 (56%) were unvaccinated, 3 (19%) had 1 dose of varicella vaccine, 3 (19%) had 2 doses of vaccine, and 1 (6%) had unknown vaccination history. Of the 8 unvaccinated cases in students attending the school, 6 had documented religious exemptions and 2 were not in compliance with vaccination requirements. Two cases had PCR testing and were positive for wild type varicella virus. One case had IgM testing and was positive. All students, parents, and staff in the school were notified of the exposures. Twenty-five students who were unvaccinated (n=24) or not in compliance (n=1) with varicella immunity requirements were excluded through 21 days after their last exposure. The DOHMH expedited shipment of varicella vaccine to the school-based health center.
CONCLUSIONS: The high number of religious exemptions at the school coupled with non-compliant students made this school highly susceptible to an outbreak and resulted in many lost days of school for unvaccinated students. In the setting of an outbreak, suspicion for varicella should remain high, even among vaccinated individuals. Routine school-based reporting is critical for rapid identification of outbreaks.