Chickenpox is a highly contagious disease caused by the varicella-zoster virus (VZV). The virus spreads easily from people with chickenpox to others who have never had the disease or never been vaccinated. If one person has it, up to 90% of the people close to that person who are not immune will also become infected. The virus spreads mainly through close contact with someone who has chickenpox.
A person with chickenpox is considered contagious beginning 1 to 2 days before rash onset until all the chickenpox lesions have crusted (scabbed). Vaccinated people who get chickenpox may develop lesions that do not crust. These people are considered contagious until no new lesions have appeared for 24 hours.
In the past, some parents participated in “chickenpox parties” to intentionally expose their unvaccinated children to a child with chickenpox in hopes that they would get the disease. CDC strongly recommends against hosting or participating in these events. Chickenpox can be serious and can lead to severe complications and death, even in healthy children. There is no way to tell in advance how severe your child’s symptoms will be. So it is not worth taking the chance of exposing your child to someone with the disease. The best way to protect infants and children against chickenpox is to get them vaccinated.
The varicella-zoster virus also causes shingles. After chickenpox, the virus remains in the body (dormant). People get shingles when VZV reactivates in their bodies after they have already had chickenpox. People with shingles can spread VZV to people who have never had chickenpox or never received the chickenpox vaccine. This can happen through direct contact with fluid from shingles rash blisters or through breathing in virus particles that come from the blisters. If they get infected, they will develop chickenpox, not shingles.
It takes about 2 weeks (from 10 to 21 days) after exposure to a person with chickenpox or shingles for someone to develop chickenpox. If a vaccinated person gets the disease, they can still spread it to others. For most people, getting chickenpox once provides immunity for life. It is possible to get chickenpox more than once, but this is not common.
For more information about how to prevent chickenpox, see Prevention and Treatment.