What Are the Facts on Chicken Pox?

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Ask the experts

Can you give me some facts about chickenpox?

Doctor's response

No problem. Here goes:

  • Chickenpox is caused by the varicella zoster virus.
  • Chickenpox is usually mild but it may be severe in infants, adults and persons with an impaired immune system.
  • Almost everyone gets chickenpox by adulthood.
  • Chickenpox is highly contagious.
  • The virus spread from person to person by direct contact, or through the air.
  • Approximately 90% of persons in a household who have not had chickenpox will get it if exposed to an infected family member.
  • Chickenpox develops within 10­-21 days after contact with an infected person.
  • Chickenpox has a characteristic itchy rash which forms blisters that dry and become scabs in 4­5 days. An infected person may have anywhere from only a few lesions to more than 500 blisters on their body during an attack (average 300­-400).
  • The rash may be the first sign of illness, sometimes coupled with fever and general malaise ("feeling lousy"), especially in adults.
  • Chickenpox is contagious 1­2 days before the rash appears and until all blisters have formed scabs.
  • Adults are more likely to have a more serious case of chickenpox with a higher rate of complications and death.
  • Every year there are approximately 5,000­9,000 hospitalizations and 100 deaths from chickenpox in the United States.
  • Varicella vaccine has been available since March 1995, and is approved for use in healthy children 12 months of age or older, and susceptible (i.e., no evidence of having had chickenpox in the past) adolescents and adults.
  • Varicella vaccine is highly effective in protecting against severe chickenpox.
  • Cases of disease due to the natural virus that may occur in a small proportion of vaccinees (people who have had the vaccine) are typically very mild with less than 50 skin blisters and no fever.
  • More than 6 million doses of varicella vaccine have been given since it was licensed in March 1995.
  • It is recommended that all children be routinely vaccinated at 12-­ 18 months of age and that all susceptible children receive the vaccine before their 13th birthday.
  • The vaccine is also approved for susceptible adolescents and adults especially those with close contact with persons at high risk for serious complications (e.g., health­care workers, family contacts of immunocompromised persons).
  • A history of chickenpox is considered adequate evidence of immunity.
  • A blood test is available to test immunity in persons who are uncertain of their history or who have not had chickenpox. Many of these persons will find that they are immune when tested and thus will not need to be vaccinated.
  • Effective medications (e.g., acyclovir) are available to treat chickenpox in healthy and immunocompromised persons (e.g, those with cancers, HIV/AIDS, receiving medications that depress the immune system).
  • These facts about chickenpox are based on information from the Centers for Disease Control and Prevention (CDC).

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Reviewed on 1/11/2018