Varicella Outbreak Surveillance in the United States, 2015–2016

BACKGROUND: Nationwide varicella outbreak surveillance was instituted in 2015 to monitor impact of the 2007 2-dose varicella vaccination recommendation in the US. Sentinel surveillance for varicella outbreaks in school settings demonstrated feasibility of outbreak surveillance. METHODS: Beginning August 2015, through CDC’s Epidemiology Laboratory Capacity funding, health departments conducted surveillance for varicella outbreaks, defined as ≥5 varicella cases in a setting within at least 1 incubation period (21 days). Health department staff collected case-based data on: outbreak setting, age, vaccination status, number of varicella vaccine doses, number of lesions, laboratory testing results, and whether cases resulted in hospitalizations and/or had complications. RESULTS: During 8/1/2015–1/7/2017, 49 jurisdictions reported 89 outbreaks (1,030 cases); 35 (39%) outbreaks occurred in schools, 16 (18%) in daycares, 37 (42%) in other settings, and 1 unknown setting. Median size and duration of outbreaks was 7 cases (range, 5–257 cases) and 29 days (0–160 days), respectively. Of 921 outbreak-associated cases with information on both age and vaccination, 68% (624) were in children aged 1–9 years and 77% (713) in unvaccinated persons. Among vaccinated patients with information on number of doses, 62% (119/192) were 1-dose varicella vaccine recipients. Among patients with information on number of lesions, 54% (414/767) had ≥50 lesions, of whom 86% were unvaccinated. Of vaccinees, 78% (79/101) with 1-dose and 76% (44/58) with 2-doses had <50 lesions (P = 0.84). Three patients were hospitalized, all unvaccinated; an additional 10 had complications (6 unvaccinated, 1 2-dose vaccinee, 3 1-dose vaccinees). Varicella was laboratory confirmed in 77 (7%) cases. CONCLUSION: Although varicella outbreaks continue to occur most often in school-aged children and among unvaccinated persons, they are small (median of 7). Vaccinated patients had more mild disease (<50 lesions) and no hospitalizations compared with unvaccinated patients. Number of lesions did not differ significantly among 1- vs. 2-dose vaccinees. Continued varicella outbreak surveillance is critical for monitoring the impact of the 2-dose vaccination policy for controlling outbreaks. DISCLOSURES: All authors: No reported disclosures.