Outbreak Identification, Investigation, and Control

Varicella outbreaks continue to occur even in settings such as schools where most children are vaccinated. However, there have been fewer outbreaks reported since the two-dose varicella vaccination program started in the United States. Also, these outbreaks have been smaller in size and shorter in duration. The majority of outbreak related cases occurred in unvaccinated people; in these outbreaks the majority of vaccinated patients had mild disease.

Prompt identification, investigation, and control of varicella outbreaks are important. Even mild cases can be contagious. CDC works with state health departments to monitor varicella outbreaks. For more information, see the Chapter on Varicella in the Manual for the Surveillance of Vaccine-Preventable Diseases.

States are encouraged to report varicella outbreaks to CDC quarterly. Sixty-four jurisdictions have been funded through CDC’s Epidemiology and Laboratory Capacity program to enhance varicella surveillance, including outbreak surveillance. This funding allows CDC to receive data on varicella outbreaks from all funded jurisdictions for better assessment of impact of the two-dose program on varicella outbreaks; better control of varicella outbreaks was a major rationale for the second dose recommendation. The worksheet, Reporting Line List for Varicella Outbreak Surveillance excel icon[3 sheets], should be submitted to CDC by a state health department. See the Instructions for Completing the Varicella Outbreak Surveillance Reporting Worksheet pdf icon[2 pages].

Varicella vaccination is recommended for preventing and controlling outbreaks of varicella.

  • People who do not have evidence of immunity to varicella should get a first or second dose of varicella vaccine as appropriate.
  • For outbreaks in preschool settings, two doses of varicella vaccine are recommended for children aged 1 to 4 years for best protection.
  • Optimally, outbreak control efforts should be implemented as soon as a case is identified. Varicella vaccination should be offered even if the outbreak is identified late. Varicella outbreaks in some settings – such as child care centers, schools, and institutions – can last months, particularly if varicella vaccination coverage is low. Thus, offering varicella vaccine during an outbreak may provide protection to people not yet exposed and shorten the duration of the outbreak.
  • People who get their first or second dose of varicella vaccine as part of outbreak control measures may be immediately readmitted to school.
  • People vaccinated with the first dose of varicella vaccine as part of outbreak control measures should be scheduled for the second dose according to the recommended interval for second dose administration.

 See Control and Investigation of Outbreaks for additional guidance on monitoring, investigating and controlling varicella outbreaks.