The virus varicella-zoster causes chickenpox. Spreading through direct contact or by airborne transmission of infected droplets, this highly contagious disease used to infect about 4 million American children per year, according to the Mayo Clinic. Recent development of a vaccine for chickenpox has made this once extraordinarily common childhood disease a vanishing phenomenon.
History
Despite the perception that chickenpox is a mild disease that is practically a normal part of childhood, the Mayo Clinic reports that each year in the United States, almost 11,000 people were hospitalized and 100 people died from chickenpox. Fortunately, in 1995, the highly effective chickenpox vaccine was licensed for use in the United States. The vaccine consists of a live but weakened (attenuated) strain of the varicella virus.
According to the Centers for Disease Control (CDC), by 2010, all states except Idaho and Wyoming required that children receive the chickenpox vaccine before entering day care or elementary school. With these measures in place, the Merck Manual estimates that annual cases of chickenpox have declined by 70 percent.
Schedule
Children usually receive their first dose of varicella vaccine between 12 and 15 months of age. This dose can be combined with the MMR (measles, mumps and rubella) vaccine and given as a MMRV injection, or it can be given separately but during the same doctor's visit. Starting in 2007, a second dose of varicella vaccine was added to the vaccination schedule, to be given between ages 4 and 6.
Older, unvaccinated children and adults who have not had chickenpox but have a high risk of being exposed to the virus can receive the vaccine in two "catch-up" doses.
Effectiveness
According to the CDC, the varicella vaccine prevents chickenpox in 70 percent to 90 percent of people who receive it. It prevents severe cases of chickenpox in 95 percent of people. Rarely, "breakthrough" infections occur in vaccinated people, causing mild cases of chickenpox with minimal numbers of spots, no fever and no complications.
Side Effects
According to the Mayo Clinic, side effects of the chickenpox vaccine are usually mild. As with other vaccines, the injection site might become swollen, red or sore. The CDC reports that some children develop a mild rash within one to three weeks of the vaccination, and that more serious complications such as fever or brain inflammation occur so rarely that it is not clear the vaccine caused them.
Risks
People with severe allergies to gelatin or the antibiotic neomycin should not get the varicella vaccine because of the risk of a serious reaction to its components. Anyone with a compromised immune system should not get the vaccine, because it contains live virus, and even this weakened form could overwhelm a faulty immune system.
According to the CDC, very rarely, a child who develops a rash after receiving the vaccine can transmit the virus to someone with a weakened immune system.
