If your child is vaccinated, it's highly likely that he'll never get chicken pox. According to the U.S. Centers for Disease Control (CDC), about 8 to 9 of every 10 people who are vaccinated get complete protection from the disease.
But even if your vaccinated child does come down with chicken pox, he'll have a much milder case than he would without the vaccine. In vaccinated people, chicken pox typically lasts only a few days, and involves fewer than 50 blisters (instead of 250 to 500), a low fever or no fever at all, and few other symptoms.
The vaccine also protects children against complications from chicken pox, which can be very serious and even fatal. Of the 3 to 4 million U.S. children who come down with chicken pox every year, 1 in 1,000 will develop complications such as severe pneumonia or a brain infection called encephalitis, and about 50 will die. Almost all children who develop chicken pox complications have not been vaccinated.
The vaccine helps protect against shingles, a painful and disfiguring rash caused by the same virus. Shingles is less common and less severe in people who have been vaccinated than in those who actually had chicken pox as children.
As with all vaccines, a certain number of children experience mild side effects. Up to 20 percent of children have pain where they received the shot, about 10 percent have a low fever, and about 4 percent develop a mild rash, which is basically a mild version of the disease itself. A few cases of severe reactions have been reported with the chicken pox vaccine, including pneumonia, and seizures leading to coma and even death. But these reactions are so rare that experts aren't sure they're connected to the vaccine.
If your child does get a mild case of chicken pox from the vaccine, there's a very slight possibility that he'll infect other family members. If you have elderly family members or immune-compromised people living in your household, call your doctor to learn how to protect them from catching the vaccine strain of chicken pox.