Welcome to the Vaccines and Immunizations website.
Skip directly to the search box, site navigation, or content.

Department of Health and Human Services
Centers for Disease Control and Prevention

Vaccines & Immunizations

Vaccines and Preventable Diseases:

Varicella Disease
Clinical Questions & Answers

Question and Answer image

General Questions

How serious a disease is varicella?

Prior to the availability of varicella vaccine, approximately 4 million cases of varicella occurred each year in the U.S. Although varicella is frequently perceived as a disease that does not cause serious illness, especially among healthy children, many persons, including healthcare providers, are not aware that an average of 10,600 (range 8,000-16,500) hospitalizations and 100 to 150 deaths due to chickenpox occurred every year in the United States before the varicella vaccine became available. The majority of the severe complications and deaths occurred in previously healthy individuals.

The availability of the varicella vaccine beginning in 1995 and its subsequent widespread use has had a major impact on reducing varicella disease. Varicella was not a notifiable disease when the vaccine was introduced, so early post-vaccine surveillance data are limited. However, in four states consistently reporting cases to the national surveillance system, rates of varicella in 2004 were 53%-88% lower compared to the pre-vaccine era. In the two varicella active surveillance sites, varicella incidence declined across all age groups, with an overall decline of ~90% from 1995-2005. Chickenpox-related hospitalizations in 2002 were 88% less compared with rates in 1994-1995; in addition, the age-adjusted rates for varicella deaths dropped 66% from 1990-2001. Deaths declined more than 90% among children 1-4 years of age and more than 70% among persons younger than 50 years of age.

Concurrently, 1-dose varicella vaccination coverage in children 19-35 months of age has steadily increased, with 88% coverage for this age group reported in 2005. Among one-dose vaccinated children exposed to VZV, the disease occurs in approximately 15%-20%. Although their disease is usually milder compared with unvaccinated children, approximately 25%-30% of one-dose vaccinated children who develop the disease will have clinical features similar to those of unvaccinated children. In the randomized clinical trial of one versus two doses of single-antigen varicella vaccine administered 3 months apart, the estimated vaccine efficacy of two doses was 98%. The two-dose regimen was also 100% efficacious against severe varicella. In 2006, the Advisory Committee on Immunization Practices (ACIP) voted to recommend routine two-dose varicella vaccination for children. The routine second dose recommendation is expected to further reduce varicella cases and severe complications of the disease.

What complications result from varicella?

The most common complications from varicella are bacterial infections of the skin and soft tissues in children and pneumonia in adults. Infections may be severe and include septicemia, toxic shock syndrome, necrotizing fasciitis, osteomyelitis, bacterial pneumonia, and septic arthritis. Other complications caused by VZV include cerebellar ataxia, encephalitis, viral pneumonia, and bleeding problems.

X-ray of Pneumonia caused by varicella

Why vaccinate children for what is usually a benign disease? Why not allow children to acquire natural infection and offer vaccine only to susceptible adolescents and adults?

Routine varicella vaccination for children is recommended for many reasons. More than 90% of cases, approximately 60% of hospitalizations, and 40% of deaths due to varicella occur in children less than 10 years of age. The majority of this morbidity and mortality is preventable by vaccination. In addition, children miss an average of 5-6 days of school when they have varicella and parents or other caregivers miss 3-4 days of work to care for sick children. The majority of adults who acquire varicella, as well as persons at high risk for severe disease who are not eligible for vaccination, contract the disease from unvaccinated children. From a societal perspective, a routine two-dose vaccination policy for children is cost-saving compared with no vaccination. Experience with vaccination programs both in the U.S. and elsewhere has consistently demonstrated that childhood vaccination programs are much more successful than those aimed at adolescents and adults.

Most importantly, it is not possible to predict who will have a mild case of chickenpox and who will have a serious or even deadly case of disease. The vaccine is safe and effective, and should be used to prevent as many cases as possible.

What is "breakthrough" disease?

A few examples of breakthrough infection

A breakthrough infection is defined as a case of wild-type varicella that occurs in a person more than 42 days after vaccination following exposure to wild-type virus. A breakthrough infection is usually mild; patients typically have low or no fever, develop fewer than 50 skin lesions, and experience a shorter duration of illness compared to unvaccinated individuals with natural infection. The rash is more likely to be predominantly maculopapular rather than vesicular. Given its modified clinical presentation, breakthrough varicella illness may be more difficult to clinically recognize by both practitioners and parents. However, 25%-30% of breakthrough cases are not mild, and patients have clinical features similar to those occurring in unvaccinated cases. The breakthrough rate in one-dose vaccinees exposed to varicella is estimated to be approximately 15%-20% and does not appear to increase with length of time since vaccination. In one study, the breakthrough rate in two-dose vaccinees was approximately three times lower than that in one-dose vaccinees.

top of page

How transmissible is a varicella breakthrough infection?

A study of transmission in a household setting found breakthrough varicella in one-dose vaccinated persons with less than 50 lesions to be one third as contagious as varicella in unvaccinated persons. However, breakthrough cases in persons with 50 or more lesions can be just as contagious as varicella in unvaccinated persons. In a randomized clinical trial that compared the efficacy of one dose of vaccine with that of two doses, the cumulative rate of breakthrough varicella during a 10-year observation period was more than three times lower among children who received two doses compared to those receiving one dose.

If a parent reports that his/her child has had breakthrough disease, should the child receive a second dose of vaccine?

Self-reported history of natural or breakthrough varicella (by adults or by parents for their children) is not a valid criterion for evidence of immunity to varicella. To limit the number of false-positive reports, ACIP recommends that evidence of immunity should be either a diagnosis of varicella by a health-care provider or a health-care provider verification of a history of disease rather than parental or self-reporting.

For persons reporting a history of breakthrough disease or presenting with atypical and/or mild disease, assessment by a physician or the physician’s designee is recommended and one of the following should be sought: a) an epidemiologic link to a typical varicella case or to a laboratory confirmed case; or b) evidence of laboratory confirmation, if testing was performed at the time of acute disease. When such documentation is lacking, persons should not be considered as having a valid history of disease because other diseases may mimic mild atypical varicella. For these individuals, a second dose of vaccine is recommended. If a health-care provider verifies the diagnosis based on the above criteria, then the second dose is not needed.

Is laboratory confirmation of varicella cases necessary?

Laboratory diagnosis of varicella is not routinely required but can be useful if confirmation of the diagnosis or determination of susceptibility is necessary. Widespread varicella vaccination has resulted in a dramatic decrease in varicella incidence. As vaccination rates continue to increase, more of the varicella cases will be occurring among vaccinated persons who may have atypical disease. This modified clinical presentation of disease makes varicella diagnosis by physicians difficult and may increase the need for laboratory confirmation.

top of page

Acyclovir Treatment Related

When is oral acyclovir treatment appropriate for someone with varicella?

Oral acyclovir therapy is not routinely recommended by ACIP or AAP for otherwise healthy children experiencing uncomplicated cases of varicella. However, AAP recommends that certain groups at increased risk of developing severe disease should be considered for oral acyclovir therapy. These high risk groups include healthy, nonpregnant persons older than 12 years of age; persons older than age 12 months with chronic cutaneous or pulmonary disorder and those receiving long-term salicylate therapy; and persons receiving short, intermittent, or aerosolized courses of corticosteroids (data are lacking but acyclovir may be considered for this group). In addition, some physicians may elect to use oral acyclovir for secondary cases within a household. For maximum benefit, oral acyclovir therapy should be initiated within the first 24 hours after rash onset.

For more information, visit the following site:
American Academy of Pediatrics article on Chickenpox Vaccine (exit)

When is intravenous acyclovir treatment appropriate for someone with varicella?

Intravenous acyclovir therapy is recommended for the treatment of primary varicella or recurrent zoster in immunocompromised children and for treatment of viral-mediated complications (e.g., pneumonia, encephalitis) of varicella in healthy persons, including pregnant women.

top of page

 Return to main Varicella Vaccination page

Non-CDC Link Disclaimer: Links to non-Federal organizations found at this site are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. The CDC is not responsible for the content of the individual organization web pages found at these links.

This page last modified on May 22, 2007
Content last reviewed on May 22, 2007
Content Source: National Center for Immunization and Respiratory Diseases

Quick Links


Safer Healthier People

Centers for Disease Control and Prevention 1600 Clifton Rd, Atlanta, GA 30333, U.S.A
Public Inquiries: 1-800-CDC-INFO (232-4636); 1-888-232-6348 (TTY)

Vaccines and Immunizations