Teresa Maupin1, Rachel Civen
2, Aisha Jumaan
3, Huiling Xiao
1, Jane Seward
3, and Laurene Mascola
2. (1) Varicella ActiveSurveillance Project, County of Los Angeles Department of Health Services, 44900 N. 60th Street West, Lancaster, CA, USA, (2) Acute Communicable Disease Control Unit, County of Los Angeles Department of Health Services, 313 North Figueroa Street Room 212, Los Angeles, CA, USA, (3) Child Vaccine Preventable Disease Branch, Epidemiology and Surveillance Division, National Immunization Program, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS E-61, Atlanta, GA, USA
BACKGROUND:
LAC has conducted population-based active surveillance for varicella disease in Antelope Valley, CA (pop. 340,000) since 1995 when varicella vaccine was licensed. By 2003, varicella cases have declined 86% compared to 1995. We describe varicella outbreaks between 1995 and 2003 to assess impact of vaccination.
OBJECTIVE:
Assess impact of varicella vaccination on varicella outbreaks in schools and daycare facilities.
METHOD:
Antelope Valley collected varicella reports from surveillance units, including all schools and daycare facilities. All reported varicella cases, defined as illness with acute onset of diffuse papulovesicular rash without other known cause, were included in the analysis. A varicella outbreak was defined as a succession of 5 or more varicella cases reported from any given school or daycare facility within 21 days of each other.
RESULT:
The number of varicella outbreaks declined 93% from 81 in 1995 to 6 in 2003. Of the 81 outbreaks in 1995, 67 (83%) were in K-12 schools and 14 (17%) were in daycare facilities, whereas in 2003 no outbreaks occurred in day care facilities.
Total outbreaks cases declined 97% from 1,332 cases (average 16 cases per outbreak) in 1995 to 40 cases in 2003 (average 7 cases per outbreak). The mean length of total outbreaks steadily declined from 61 days in 1995 to 31 days in 2003. The decline in outbreaks resulted in a reduction of 97% (from 7,255 to 235) school days missed, and 98% (1,178 to 25) parental work days lost in 2003 compared to 1995. Breakthrough varicella (those occurring >42 days after receipt of varicella vaccine) comprised 1% (8/1068) of outbreak cases in 1996 and 50%(20/40)in 2003.
CONCLUSION:
The number of outbreaks, the number of children affected per outbreak and the duration of the outbreaks declined steadily since the introduction of the varicella vaccination program. This resulted in fewer school days missed and fewer parental work days lost. No outbreaks occurred in daycare centers in 2002 or 2003 where vaccination coverage is expected to be highest.
LEARNING OBJECTIVES: