What is chickenpox?

Short Answer

Chickenpox is a very contagious, viral disease that causes a range of symptoms including a blister-like rash, itching, tiredness, and fever. It is spread by touching or breathing in the virus particles that come from chickenpox blisters. While chickenpox is usually thought of as a childhood illness that’s pretty common, it can lead to serious complications and even death. There is currently a vaccine for chickenpox. One dose of the vaccine is 70-90% effective in preventing disease, but two doses are over 98% effective.




Symptoms & Incubation

Chickenpox is a disease caused by the varicella zoster virus. It appears as itchy blisters that start on the face, chest, back, and stomach. The rash can spread over the whole body, even inside the mouth. Chickenpox also causes fever, headache, and tiredness. People are usually sick for five to 10 days. It’s still possible to get chickenpox if you have been vaccinated against the disease, but it is usually a milder form with fewer blisters and little or no fever. Most children with chickenpox completely recover in a week, but the itching can be very uncomfortable. Children with chickenpox will likely miss several days of school or child care. It takes between 10 and 21 days after coming in contact with the varicella virus for someone to develop chickenpox.


Serious complications from chickenpox include dehydration, pneumonia, bleeding problems, infection or inflammation of the brain (encephalitis, cerebellar ataxia), bacterial infections of the skin and soft tissues in children including Group A streptococcal infections, bloodstream infections (sepsis), toxic shock syndrome, bone infections, and joint infections.

Some people with serious complications from chickenpox can become so sick that they need to be hospitalized. Chickenpox can also be fatal, even in healthy children and adults who are unvaccinated. Many of the healthy adults who die from chickenpox contract the disease from their unvaccinated children.


Chickenpox spreads easily through the air when an infected person coughs or sneezes. It can also spread by touching fluid from blisters. A person with chickenpox can spread the disease from one to two days before they get the rash until all their chickenpox blisters have formed scabs. Infected children should stay out of school or child care for at least a week to avoid spreading the virus to others. If a person who was vaccinated for chickenpox gets the disease, they are still infectious.

High-risk Populations

Chickenpox can be especially serious for babies, adolescents, adults, pregnant women, and people with weakened immune systems.


The chickenpox vaccine is a live attenuated vaccine, which means that the live, disease-producing varicella virus was modified to create the vaccine. One dose of the vaccine is 70-90% effective in preventing disease, but two doses are over 98% effective (MMWR June 22, 2007). Some vaccinated children do get chickenpox, but symptoms are usually mild. Vaccinated children who get varicella will have fewer blisters and are less likely to have a fever.

In 2005, a combination vaccine containing live attenuated measles-mumps-rubella and varicella (MMRV) vaccine was licensed for use in children ages 12 months through 12 years. It was created to reduce the number of shots children get.

Safety & Side Effects

The chickenpox vaccine is very safe, and it is effective at preventing chickenpox. Vaccines, like any medicine, can have side effects. Most people who get the chickenpox vaccine have no side effects. Possible side effects from the single varicella vaccine include redness, stiffness and soreness at the injection site, and some people develop a mild rash. Side effects from the MMRV combination vaccine are rare, but could include fever and fever-related seizures, so the CDC recommends that children between ages 1 to 4 be given separate MMR and varicella shots. MMRV is preferred over separate injections for children ages 4 through 12 years.


Children need two doses of the vaccine at the following ages for best protection:

The first dose at 12 through 15 months; and
A second dose at 4 through 6 years of age.

Since the Vaccine Was Introduced…

Before the chickenpox vaccine was licensed in the United States in 1995, about four million people got chickenpox each year. Also, about 10,600 people were hospitalized and 100 to 150 died each year as a result of chickenpox. Since the vaccine was introduced, the number of hospitalizations and deaths from chickenpox has declined by more than 90 percent.