Isolating an infected person from others until the disease is no longer contagious is perhaps the most well-known preventative measure. The most effective way to prevent an initial infection to chickenpox is to be vaccinated.

Varicella (chickenpox) vaccine is nearly always safe and effective when it is administered correctly. It is believed to be effective at preventing infection for at least 10 to 20 years. Fever and mild chickenpox rash may follow vaccination in some patients. Pain, swelling and redness may also occur at the injection site. Although it is extremely rare, serious side effects (e.g., seizures, pneumonia) can also occur.

Children have been routinely vaccinated for varicella-zoster virus (VZV) since it was approved by the U.S. Food and Drug Administration (FDA) for use in 1995. It is usually given while a child is between the ages of 1 and 12. The vaccine is often given during the same visit as the measles-mumps-rubella (MMR) vaccine. Older individuals without immunity, who have never contracted the disease, may also be immunized.

On a few rare occasions, a person who has received the chickenpox vaccine has contracted the virus. In these rare instances, the person usually has more mild symptoms than if they had not been immunized. Typically, people who were vaccinated develop no more than 50 spots, and the spots rarely become blisters. It is possible for these people to infect others with the disease. However, this is extremely rare.

Ongoing research is currently being conducted to gauge if additional booster doses may be necessary later in life. In June 2006, the Advisory Committee on Immunization Practices (ACIP) to the Centers for Disease Control and Prevention (CDC) recommended a second dose of the varicella vaccine be given to children ages 4 to 6 to boost protection against the disease. The Committee also recommended a second dose for older children, adolescents and adults who have previously received an initial dose. Patients who are concerned about the effectiveness of their varicella vaccine should consult their physician.

Though effective, the chickenpox vaccine is not appropriate for everyone. For instance, the vaccine is not recommended for pregnant women. Women should not become pregnant for one month after receiving the vaccine. It is safe for women to receive the vaccine after delivering their baby.

Additional populations for which the vaccine is not approved include:

• Infants younger than one year of age
  
  
• People with weakened immune systems (e.g., cancer patients)
  
  
• People allergic to gelatin or the antibiotic neomycin
  
  
• People taking high doses of certain immune system suppressing medications (e.g., corticosteroids)

People with moderate or severe illness may also be advised to postpone the shot until they recover.

In addition, acyclovir, varicella zoster immune globulin (VZIG) or the vaccine can also be given to susceptible individuals (e.g., pregnant women, children with weakened immune systems) after exposure to the VZV in an attempt to guard against infection. Each may be effective at preventing infection up to several days following exposure to VZV. Individuals with a compromised immune system who believe they have been exposed to the chickenpox virus should immediately contact their physician.

Although it is considered safe for people who have already had the disease to receive the varicella vaccine, there is a blood test available to help determine whether a patient has had chickenpox or not.