Monitoring the Impact of Varicella Vaccination

Chickenpox used to be very common in the United States. In the early 1990s, an average of 4 million people got varicella, 10,500 to 13,000 were hospitalized (range, 8,000 to 18,000), and 100 to 150 died each year. In the 1990s, the highest rate of varicella was reported in preschool-aged children.

Chickenpox vaccine became available in the United States in 1995. In 2014, 91% of children 19 to 35 months old in the United States had received one dose of varicella vaccine, varying from 83% to 95% by state. Among adolescents 13 to 17 years of age without a prior history of disease, 95% had received 1 dose of varicella vaccine, and 81% had received 2 doses of the vaccine. Eighty-five percent of adolescents had either a history of varicella disease or received 2 doses of varicella vaccine.

Each year, more than 3.5 million cases of varicella, 9,000 hospitalizations, and 100 deaths are prevented by varicella vaccination in the United States.

• Varicella incidence, based on national passive surveillance data published in 2012, declined 79% during 2000-2010 in 31 states that met CDC’s criteria for adequate and consistent reporting. From this same data source, incidence declined 72% during 2006-2010, after a routine second dose of varicella vaccine was recommended. Varicella incidence from 2 active surveillance sites declined 98% during 1995-2010.
• Varicella outbreaks declined 78%, from 147 in 2005 to 33 outbreaks in 2012 based on passive surveillance data from 6 states. Varicella outbreaks from one active surveillance site declined 95%, from 236 outbreaks during 1995 to 1998 to 12 outbreaks during 2007 to 2010. Outbreaks also decreased in size (as measured by number of varicella cases per outbreak), and duration.
• Varicella-related outpatient visits declined 84% in 2012 versus the prevaccination period (1994-1995) with 95% decline among infants aged <1 year and 75%-89% decline among persons aged 1-49 years.
• Varicella hospitalizations declined 93% in 2012 versus the pre-vaccine period; during the 2-dose varicella vaccination period (2006-2012), hospitalizations declined38%
• Varicella deaths declined by 87% during 2008 to 2011 as compared to 1990 to 1994 based on data from the National Center for Health Statistics (NCHS). In children and adolescents less than 20 years of age, varicella deaths declined by 99% during 2008 to 2011 as compared with 1990 to 1994.
• Varicella incidence among HIV-infected children declined 63% during 2000-2007 compared to 1989-1999.
• Varicella vaccination provides indirect benefits to people who are not eligible for vaccination. Varicella incidence among infants, a group not eligible for varicella vaccination, declined by 90% from 1995 to 2008.

CDC is monitoring the effects of varicella vaccination on the epidemiology of herpes zoster in the United States. Studies indicate that overall rates of herpes zoster appear to be increasing, however, introduction of the varicella vaccine does not seem to be affecting this increase. Although uncommon in children, the rate of herpes zoster in United States children has been declining since the routine varicella vaccination program began. Perhaps because vaccinated children are less likely to become infected with wild-type chickenpox virus, which is more likely to reactivate as shingles compared to attenuated vaccine virus.