MMWR: Varicella Surveillance
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Since varicella first became nationally notifiable in 1972, surveillance practices for varicella have changed and evolved. The history of varicella surveillance was discussed in the Center for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report [2102;61(32);609-612].
National varicella surveillance has improved greatly since 1976, when the vaccine was first recommended. With declines in varicella incidence after 1 dose of varicella vaccine was added to the routine childhood vaccination schedule in 1996 and a second dose was recommended in 2006, the number of cases of varicella in the active surveillance sites has become insufficient to monitor further impact of vaccination.
Between 2000 and 2010, the CDC evaluated varicella surveillance data reported via the National Notifiable Diseases Surveillance System (NNDSS) to determine whether these data might now be adequate for monitoring vaccination impact.
Varicella incidence in the states that met these criteria declined 79% overall, from 43 per 100,000 population in 2000 to 9 in 2010. While 1 dose of varicella vaccine was recommended, incidence declined 43% from 2000 to 2005, and after a second dose was added to the routine childhood schedule, incidence declined 72% from 2006 to 2010. State varicella surveillance data reported to the CDC through the NNDSS are now adequate for monitoring trends in varicella incidence, but continued strengthening of the surveillance system and participation of all states is needed.
In 2000, a total of 12 states required reporting of varicella cases to the state, 2 states were conducting passive case-based surveillance, and 10 were conducting aggregate reporting; 10 states had adequate and consistent reporting. By 2010, a total of 39 states had made varicella reportable to the state, 38 states were conducting passive case-based surveillance, and 31 had adequate and consistent reporting.
Overall incidence in the states that met adequate and consistent reporting criteria declined 79.4%, from 43.2 per 100,000 in 2000 to 8.9 in 2010. During 2000 to 2005, when a single dose of varicella vaccine was recommended, incidence declined 43.3%; during 2006 to 2010, when 2 doses were recommended routinely, incidence declined a further 71.6%.
As an additional criterion, states were asked in 2010 when they first considered their varicella reporting to the CDC to be reliable (considered reliable by the reporting state). Twenty-six of the 31 states with adequate and consistent reporting responded; all 26 stated that they considered their varicella data reported to the CDC in 2010 to be reliable. Overall incidence in these 26 states declined 81.8% from 2000 to 2010, 45.4% from 2000 to 2005, and 77.4% from 2006 to 2010.
Based on data from 28 states, from 2000 to 2010, varicella incidence declined most among children 1 to 4 years of age (69.7%) and 5 to 9 years of age (86.2%), the age groups for whom 1 dose of vaccine was routinely recommended during 2000 to 2005 and 2 doses were recommended during 2006 to 2010. During 2000 to 2005, age-specific incidence declined 37.4% and 49.8% among children 1 to 4 and 5 to 9 years of age, respectively. Declines continued during 2006 to 2010, when 2 doses were recommended, with incidence in children 1 to 4 and 5 to 9 years of age decreasing 59.3% and 82.3%, respectively.