Vaccination

A live-virus vaccine (Varivax) produces persistent immunity against chickenpox. Data show that the vaccine can prevent chickenpox or reduce the severity of the illness if it is used within 3 days, and possibly up to 5 days, after exposure to the infection.

The vaccine against chickenpox is now recommended in the U.S .for all children between the ages of 18 months and adolescents who have not yet had chickenpox. Children are given one dose of the vaccine. (A new vaccine [Proquad] for children ages 1 – 12 years combines measles, mumps, rubella, and varicella in one product.) Two doses, 1 to 2 months apart, are given to children age 13 years and older.

Recommendations for the Vaccine in Adults

The U.S. Centers for Disease Control and Prevention (CDC) recommends that every healthy adult without a known history of chickenpox be vaccinated. Adults in the following groups should strongly consider vaccination:

• Those with high risk of exposure or transmission (hospital or day care workers, parents of young children).
• People in contact with those who have compromised immune systems.
• Nonpregnant women of childbearing age.
• International travelers.

As with other live-virus vaccines, the chickenpox vaccine is not recommended for:

• Women who are pregnant or who may become pregnant within 30 days of vaccination.
• People whose immune systems are compromised by disease or drugs (such as after organ transplantation). Experts report that the vaccine is safe in children with acute lymphoblastic leukemia (ALL). Certain children who are HIV-positive may be candidates for the vaccine. An inactivated chickenpox vaccine may be safe for patients undergoing bone marrow transplants when given before and after the operation.

Patients who cannot be vaccinated but who are exposed to chickenpox receive immune globulin antibodies against varicella virus. This helps prevent complications of the disease if they become infected.

Side Effects of the Varicella (Chickenpox) Vaccine

• Discomfort at the Injection Site. About 20% of vaccine recipients have pain, swelling, or redness at the injection site.
• Severe Side Effects. Only about 5% of adverse reactions are serious. Such events include seizures, pneumonia, anaphylactic reaction, encephalitis, Stevens-Johnsons syndrome, neuropathy, herpes zoster, and blood abnormalities.
• Risk of Transmission. The vaccine may produce a mild rash within about a month of the vaccination, which can transmit chickenpox to others. Individuals who have recently been vaccinated should avoid close contact with anyone who might be susceptible to severe complications from chickenpox until the risk for a rash passes.
• Later Infection. Months or even years after the vaccination, some people develop a mild infection termed modified varicella-like syndrome (MVLS). The condition appears to be less contagious and has fewer complications than naturally acquired chickenpox.

Vaccine Long-Term Effectiveness and Possible Need for a Booster

There is currently intense debate over the long-term protection of the vaccine. Such controversy is stimulated by the incidence of breakthrough infections after vaccination. However, evidence clearly shows  improvements in quality of life and better survival rates since the introduction of the vaccine. Any negative studies to date on long-term effectiveness simply raise the question of the need for booster or higher doses -- not the elimination of the vaccine altogether.

Breakthrough Infections and Waning Protection in Vaccinated Children. Studies report that more than 15% of vaccinated children still develop chickenpox (called breakthrough infections). Reasons for this include:

• Waning Immunity. Studies on children in day care centers report that nearly half of children who had been previously vaccinated develop chickenpox. In one study, children vaccinated within three years had a much lower risk than those whose vaccinations had occurred later. Another study reported a higher risk for breakthrough infections in children who were immunized before 15 months.
• Oral Steroids. Children on oral steroids are also at higher risk for a breakthrough infection. (Children taking inhaled steroids, such as for asthma, do not appear to have this risk.)

If vaccinated children develop chickenpox, the cases are nearly always mild and usually less contagious. In such children, the infection appears to be caused by a wild virus, not a reactivation of the vaccine.

This does not necessarily mean that children who are vaccinated eventually lose total immunity. A breakthrough infection is often due to issues with the primary vaccine (improper storage, low potency) or the child's history (having asthma, being less than 14 months at the time of vaccination). Nevertheless, some evidence suggests that either having the vaccination or even having chickenpox itself is not as protective against a later infection as experts have previously thought.

Long-Term Protection in Vaccinated Adults. The protective effect for adults is even less clear. An encouraging study of adults reported that although 9% developed chickenpox months to years after their last vaccination, in all cases, infection was mild, with none of the serious complications of adult chickenpox. A 2003 study on booster shots in older adults suggests that revaccination with the live virus is safe and effective.

Vaccine's Effect on Shingles. It is not yet clear if the chickenpox vaccine protects against the later development of shingles. Vaccination began in 1995, so it may take years for scientists to better understand its effect on shingles. However, in 2006 a shingles vaccine was approved for use in the United States. The zoster vaccine (Zostavax) is a stronger version of the chickenpox vaccine. Study results published in 2005 suggested that the zoster vaccine could prevent about half of all shingles cases and two-thirds of postherpetic neuralgia cases. The vaccine was tested in adults age 60 years and older.

Varicella-Zoster Immune Globulin

Varicella-zoster immune globulin (VZIG) is a substance that triggers an immune response against the varicella-zoster virus. It is used to protect high-risk patients who are exposed to chickenpox, or those who cannot receive a vaccination of the live virus. Such groups include:

• Pregnant women with no history of chickenpox
• Newborns under 4 weeks who are exposed to chickenpox or shingles
• Premature infants
• Immunocompromised children and adults with no antibodies to VZV
• Recipients of bone-marrow transplants (even if they have had chickenpox)
• Patients with a debilitating disease (even if they have had chickenpox)

VZIG should be given within 96 hours and no later than 10 days after exposure to someone with chickenpox.