The chickenpox vaccine is a shot that can protect nearly everyone who gets it from catching chickenpox. It's also called the varicella vaccine, because chickenpox is caused by the varicella-zoster virus. The vaccine is made from a live but weakened, or attenuated, virus.
Viruses that have been attenuated are less virulent than viruses that are not. Although the virus in the chickenpox vaccine is generally incapable of causing a disease, it still stimulates a response from the body's immune system. That response is what gives someone who's had a shot for chickenpox immunity or protection from the illness.
Why Do People Need a Chickenpox Vaccine?
Most cases of chickenpox are relatively mild and run their course in five to 10 days. But it can be very serious, even life-threatening, in a small percentage of people. Before the varicella vaccine was licensed in the U.S. in 1995, there were approximately 100 deaths and more than 11,000 hospitalizations a year from chickenpox. Most of the people who died were healthy before they got chickenpox.
The risk of serious, life-threatening complications is greatest among infants, adults, and people with weakened immune systems. But anyone can develop serious complications and there is no way to predict who will.
There's another reason for getting a shot for chickenpox. The illness is highly contagious and can be spread by direct contact or through the air by sneezing or coughing. Also, someone can get it by coming in contact with fluid from chickenpox blisters. For that reason, children with chickenpox need to be kept out of school or day care for about a week or more until all blisters have dried and crusted over. The illness causes an itchy rash that usually forms between 200 and 500 blisters over the entire body, headaches, coughing, and fussiness. So even if the illness is mild, it still means five to 10 days of being uncomfortable.