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Chickenpox is a highly contagious disease caused by the varicella-zoster virus (VZV). It can cause an itchy, blister-like rash. Chickenpox can be severe, especially in babies, adolescents, adults, pregnant women, and people with a weakened immune system.

Varicella, the infectious viral disease that causes chickenpox, was often confused with smallpox until around 1875. A scientist named Steiner showed the difference by inoculating patients using fluid from people already infected.  Scientists use cell cultures to try and separate from these fluids whereby in 1954, varicella was isolated. Lab tests continued throughout the 20th century. In the 1970s, a lab in Japan successfully isolated the vaccine. In 1995, the chickenpox vaccine became licensed for widespread use in the United States, and the booster dose was added in 2006.


It is available as a single vaccine, and as part of the MMRV vaccine (measles, mumps, rubella, and varicella vaccine).


Children under age 13 years should get two doses.

  • First dose at age 12 through 15 months

  • Second dose at age 4 through 6 years

The second dose may be given at an earlier age if given at least three months after the first dose.

Serious complications from chickenpox may include:

  • Bacterial infections of the skin and soft tissues in children

  • Infection of the lungs (pneumonia)

  • Infection or swelling of the brain (encephalitis)

  • Bleeding problems (hemorrhagic complications)

  • Bloodstream infections

  • Dehydration

Some people with severe complications from chickenpox can become so sick that they need to be hospitalized. Chickenpox can also cause death. Deaths are infrequent now due to the vaccine program. However, some deaths from chickenpox continue to occur in healthy, unvaccinated children and adults

Chickenpox used to be very common in the United States. In the early 1990s, an average of 4 million people got chickenpox, 10,500 to 13,000 were hospitalized, and 100 to 150 died each year.

An itchy blister rash appears 10 to 21 days after exposure to the virus and usually lasts about five to 10 days. Other symptoms, which may appear one to two days before the rash, include:

  • Fever

  • Loss of appetite

  • Headache

  • Tiredness and a general feeling of being unwell 

Once the chickenpox rash appears, it goes through three phases:

  1. Raised pink or red bumps, which break out over several days

  2. Small fluid-filled blisters, which form in about one day and then break and leak

  3. Crusts and scabs, which cover the broken blisters and take several more days to heal

The virus can be spread to other people for up to 48 hours before the rash appears, and the virus remains contagious until all broken blisters have crusted over.

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