The 130th Annual Meeting of APHA

Abstract #46229

Donovan Robinson, MPH¹, Karl Heath, RN, GCP¹, Dana Perella, BS Microbiology¹, and Barbara Watson, MD². (1) Immunization Program, Philadelphia Department of Public Health, 500 S. Broad, Philadelphia, PA 19146, 215-685-6838, donovan.robinson@phila.gov, (2) Divison of Disease Control, Philadelphia Department of Public Health, 500 S. Broad Street, Philadelphia, PA 19146

Background: Varicella vaccine was licensed in May 1995 and required for entry to childcare. The vaccine effectiveness (VE) in some recent outbreaks has ranged from 42% in New Hampshire to 84% in Massachusetts against any varicella disease and higher against severe disease.

Objective: To examine VE and risk factors for development of disease during the childcare center outbreak.

Methods: Demographics, varicella susceptibility, preexisting conditions, and attendance patterns were collected from childcare center reports, healthcare records, and self-administered questionnaires given to the 25 staff and parents of all the 154 attendees. Detailed clinical and epidemiologic information was obtained for all cases.

Results: According to preliminary varicella susceptibility information, 22 of the 179 (12.3%) childcare center attendees and staff had a history of varicella disease, 1 (0.6%) staff member had a positive varicella-zoster virus antibody titer, 1 (0.6%) attendee had a history of Herpes zoster following vaccination, 137 (76.5%) attendees had received the varicella vaccine; 18 (10.1%) had no history of disease and had not received the varicella vaccine; and 1 (0.6%) staff member’s varicella susceptibility status was uncertain. The index case was a 4-year-old unvaccinated male attendee who developed a mild varicella rash (<50 lesions) on September 26, 2001. A total of 21 cases occurred during the 16-week outbreak, and breakthrough infection occurred in 14 (66.7%) of the varicella cases. VE for the childcare center outbreak was 74% (95% CI: 44% - 88%).

Conclusions: VE reflects similar levels to previous studies. Unvaccinated children put other children at risk even in childcare settings with high vaccination compliance.

Learning Objectives:

• Describe the epidemiology of a varicella outbreak in a preschool setting with high vaccination compliance.
• Evaluate the effect of varicella susceptible children on the introduction and spread of the disease in the preschool.
• Identify the vaccine effectiveness (VE) in relation to varicella outbreaks previously studied.

Keywords: Outbreaks, Immunizations

Presenting author's disclosure statement:
Organization/institution whose products or services will be discussed: The sole manufacturer of varicella vaccine for use in the US is Merck. Post exposure vaccination as an outbreak control measure is not currently approved by the FDA but is recomended by the CDC in MMWR.
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.