Varicella Outbreak In a Daycare During the 2-Dose Vaccination Era

Background: Since 2002, daycare outbreaks have been rare due to the impact of varicella vaccination (VV). Further reduction in disease among younger children (<4 years old) has been seen following implementation of the 2-dose requirement for school entry. For varicella outbreak control, the Philadelphia Department of Public Health (PDPH) recommends exclusion of individuals with rash and children under-immunized with immunization as well as post-exposure vaccination.   

Objectives: To describe a varicella outbreak in a daycare setting during the 2-dose vaccination era and the role of under-immunized attendees in disease transmission.  

Methods: In fall 2010, PDPH staff investigated a varicella outbreak at a daycare serving a multi-lingual community. Demographics, vaccination status, varicella disease history, languages spoken at home and birth country were collected for all daycare attendees, staff, and parents when applicable, and clinical data were collected for all cases.  

Results: All 26 daycare attendees aged 12-32 months had foreign-born or multilingual parents. Before the outbreak, 18 (69%) had received VV dose 1 and 8 (31%) were unvaccinated. Of those unvaccinated, 4 had parents/guardians who were religiously/philosophically opposed to vaccinations, 3 with recent 1^st birthdays had not had the 12-month well visit, and 1 reported varicella history. The index case was in an unvaccinated 15-month old who attended daycare with rash due to a missed varicella diagnosis. Two weeks later, 3 unvaccinated individuals (2 attendees, 1 staff) and 1 vaccinated attendee developed varicella. As a result, 2 attendees with no VV were excluded. Subsequently, another 2 cases occurred in unvaccinated individuals who were not excluded.

Conclusions: This outbreak underlines the importance of enforcement of immunization regulations in daycares and of immunization timeliness at the 12-month visit. Additional effort is required to reach communities prone to development of pockets of under immunization.