Immunizations - Varicella-Zoster Virus (Chickenpox)

Varicella-Zoster Virus (Chickenpox):

Chickenpox (caused by the varicella-zoster virus) is one of the most contagious childhood diseases. Nearly every unvaccinated child becomes infected with it. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts.

The infection rarely causes complications in healthy children, but it is not always harmless. Five out of every 1,000 children are hospitalized and, in rare cases, it can be fatal. Before the vaccination became widespread, chickenpox resulted in about 11,000 hospitalizations and 100 deaths a year.

This is a close-up picture of chickenpox. Early chickenpox lesions consist of small red papules that quickly fill with a yellowish or straw colored fluid to form small blisters (vesicles), as seen in this photograph. Later, these vesicles will rupture, forming shallow erosions that crust over and then ultimately heal.

Chickenpox can be especially severe in adults and very serious in anyone with a compromised immune system. In addition, the varicella virus (which persists after the childhood disease) erupts as a painful and distressing condition called herpes zoster (shingles) in about 20% of adults with a history of chickenpox. Chickenpox itself usually occurs only once, although a few cases of mild second infections, marked by the telltale rash, have been reported in older children years after their first infection.

Vaccines for Chickenpox

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 even if it is used within 3 days, and possibly up to 5 days, after exposure to the infection.

Recommendations for the Vaccine in Children. The vaccine against chickenpox is now recommended in the U.S. for all children between the ages of 18 months and adolescence who have not yet had chickenpox. Children are given one dose of the vaccine. Two doses 1 - 2 months apart are given to people over 13 years of age. To date, more than 75% of children have been vaccinated.

Doctors recommend that the chickenpox vaccine be given at the same time as the measles-mumps-rubella (MMR) vaccine or that there is a delay of at least 1 month between the two vaccinations. (If the chickenpox vaccination is given within that 30-day period -- but not at the same time -- there is a higher risk for a breakthrough infection later on.)

A chickenpox vaccine is part of the routine immunization schedule. It is about 100% effective against moderate or severe illness, and 85 - 90% effective against mild chickenpox. Parents often express concern that the immunity from the vaccine might not last. The chickenpox vaccine, though, is the only routine vaccine that does not require a booster.

Recommendations for the Vaccine in Adults.

Some doctors suggest that every healthy adult without a known history of chickenpox be vaccinated. In general, however, the following adults should consider vaccinations:

• Older people without a history of chickenpox and who are at high risk of exposure or transmission (such as hospital or day care workers and parents of young children)
• People who live or work in environments in which viral transmission is likely
• Nonpregnant women of childbearing age
• Adolescents and adults living in households with children
• International travelers

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

• Pregnant women (including the 3 months prior to pregnancy). Of note, an encouraging study suggested that pregnant women who were inadvertently vaccinated did not face a higher risk for birth defects in their offspring.
• People whose immune systems are compromised by disease or drugs (such as after organ transplantation). The vaccine is being studied, however, for its safety in some of these patients, particularly children with cancer or other high-risk conditions. Experts report that it is safe in children with acute lymphoblastic leukemia (ALL), who should receive two doses. Certain children who are HIV positive may be candidates for the vaccine. An inactivated varicella vaccine may be safe and effective in patients undergoing bone marrow transplants, when given before and after the operation.
• Most patients who cannot be vaccinated but are exposed to chickenpox are given immune globulin antibodies against varicella virus. This helps prevent complications of the disease if they become infected.

Side Effects of the Chickenpox Vaccine

Discomfort at the Injection Site. About 20% of vaccine recipients have pain, swelling, or redness at the injection site.

Mild Rash and Risk of Transmission. The vaccine may produce a mild rash within about a month of the vaccination, which has been known to 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 has passed.

Severe Side Effects. Between 1995 and 2001, 759 serious adverse effects were reported. Such events included seizures, pneumonia, anaphylactic reaction, encephalitis, Stevens-Johnson syndrome, neuropathy, herpes zoster, and blood abnormalities. Anecdotal reports have found a higher association of side effects when varicella vaccine is given at the same time as the measles, mumps, and rubella (MMR) vaccination. Because combined vaccinations are being developed, such effects should be closely studied.

Long-Term Protection and Booster Shots

There is intense debate over the long-term protection of the vaccine. The incidence of breakthrough infections after vaccination stimulates the controversy. It should be noted, however, that evidence is showing 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.

Long-Term Protection in Vaccinated Children. Most studies suggest that the vaccine is not wholly effective in up to 30% of vaccinated children. However, they also report if chickenpox occurs, more than 95% of the cases are mild. It is also usually less contagious. In such people, the infection appears to be caused by a wild virus, not a reactivation of the vaccine. (Of concern was a 2002 study of a day care center reporting a much higher rate -- 56% -- of break-through infection, with only 86% of cases being mild. The implications of this study are unclear.) The longer the interval since vaccination occurs, the higher the risk for a breakthrough infection.

This does not necessarily mean, however, 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, the duration between the chickenpox and measles, mumps, and rubella vaccines being less than a month) or the child's history (having asthma, being less than 14 months at the time of vaccination). Nevertheless, there is also some evidence that either having the vaccination or even having chickenpox itself is not as protective against a later infection as experts have thought.

Long-Term Protection in Vaccinated Adults. The protective effects for adults are even less clear. An encouraging 2002 study of adults vaccinated between 1979 and 1999 reported that 9% developed chickenpox months to years after their last vaccination. The length of time since the vaccination did not seem to affect whether the adults would catch chickenpox or not. (Nearly half of those had been exposed to the disease in their homes.) In all cases, infection was mild, with none of the serious complications of adult chickenpox.

Vaccine's Effect on Shingles. A primary concern is whether the vaccine protects against shingles later on, particularly in people who have breakthrough infections -- however mild. As more and more children get vaccinated, the actual protection of the vaccine and the implication of the breakthrough infection will become clearer.

[For more information, see In-Depth Report #82: Shingles and chickenpox (Varicella-zoster virus).]

In September, 2005, the Food and Drug Administration approved a combination vaccine to protect against measles, mumps, rubella, and chickenpox. Proquad, produced by Merck & Co., protects against all four infections with one shot, thus sparing young children from multiple painful injections. Proquad is approved for use in children from 12 months to 12 years of age. Proquad was studied in four randomized trials involving 5,446 healthy children aged 12 - 23 months received Proquad. Proquad’s immune response rates were 97.4% for measles, 95.8 - 98.8% for mumps, 98.5% for rubella, and 91.2% for chickenpox, similar to the rates induced by the concomitant administration of single doses of M-M-R II and Varviax at separate injection sites in 2,038 children.