Outbreaks

Data on the number of chickenpox (varicella) outbreaks that occur each year in the United States are lacking. But, since the chickenpox vaccine was introduced, the number of outbreaks has gone down as documented in one of the varicella active surveillance sites during 1995-2010 and in 6 states that reported outbreak data to CDC during 2005-2012..

Chickenpox outbreaks continue to occur even in settings such as schools where most children are vaccinated. However, there have been fewer outbreaks reported ever since the two-dose chickenpox vaccination program started in the United States. Also, these outbreaks have been smaller. The vaccine may not prevent all chickenpox, but it is very effective at preventing severe cases.

Outbreak Surveillance, Investigation, and Control

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

States are encouraged to report chickenpox outbreaks to CDC quarterly. Starting in 2015, 48 jurisdictions have been funded through CDC’s Epidemiology and Laboratory Capacity program to enhance varicella surveillance, including outbreak surveillance. This funding will allow CDC to receive data on varicella outbreaks from all funded jurisdictions to allow better assessment of impact of the second dose program on varicella outbreaks, which was a major rationale for the second dose recommendation. The worksheet, Reporting Line List for Varicella Outbreak Surveillance [3 sheets], should be submitted to CDC by a state health department. See the Instructions for Completing the Varicella Outbreak Surveillance Reporting Worksheet [2 pages].

Preventing and Controlling Chickenpox Outbreaks

Chickenpox vaccination is recommended for preventing and controlling outbreaks of chickenpox.

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

Guidelines and Resources

• Control & Investigation of Varicella Outbreaks
• Reporting Line List for Varicella Outbreak Surveillance [3 sheets] worksheet
• Instructions for Completing the Varicella Outbreak Surveillance Reporting Worksheet [2 pages]
• Specimen Collection Form