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A recent study found that the chickenpox vaccine has been successful in decreasing the virus among children. Dr. Sandy Arnold, a pediatric infectious disease specialist at Le Bonheur Children’s, explains the study published in the journal Pediatrics, chickenpox and the need for the vaccine.

First of all, let’s talk about the vaccine.

Varicella zoster virus is the name of the virus that causes chickenpox. Varicella vaccine, which prevents chickenpox, is a live, attenuated virus vaccine. This means that the virus in the vaccine is alive but has been changed through laboratory means so that it will not cause infection. This allows the virus to grow once injected and stimulate the immune system to cause immunity without causing illness.

How long has the vaccine been in use?

Varicella vaccine was approved for use in children older than 1 year of age in the U.S. in 1995. It had been used in Japan, where it was developed, for many years prior to this.

Why was the vaccine developed?

The reason the vaccine was developed was that most children were infected with the virus in childhood, and many developed complications requiring hospitalization or, more rarely, death each year. Although in most children, chickenpox is a mild illness with fever and a rash of small blisters (or vesicles) all over the skin, it can affect any organ of the body and lead to bacterial infections. Complications can include:

• skin infections that can be severe and life threatening
• pneumonia
• hepatitis
• meningitis
• encephalitis
• bone and joint infections
• post-viral cerebellar ataxia – a condition where the child has balance trouble due to inflammation in the brain

Also, chickenpox belongs to a family of viruses that stay in your body forever after an infection. As a result, you can have a reactivation of the virus, which is called shingles or herpes zoster if your immune system is impaired or as you get older.

Before the introduction of this vaccine, there were 4 million cases of chickenpox per year in the U.S., 10,000 related hospitalizations and 100 deaths each year. After the vaccine was approved, it was recommended to be given as a single dose after the first birthday. As a result, the rate of chickenpox illness in the U.S. decreased by 90 percent between 1995 and 2005.

Why are two doses required for the chickenpox vaccine?

Despite the decrease in illnesses, outbreaks of chickenpox continued to occur even among children who had been vaccinated. This occurred because approximately 15-20 percent of children have an inadequate response to varicella vaccine, and vaccinated children with breakthrough varicella (varicella occurring in vaccinated children) are contagious. This led the ACIP (Advisory Committee on Immunization Practices) to recommend that all children receive two doses of varicella vaccine with the second dose occurring at 4 to 6 years of age, when other preschool vaccines are given.

Why is it necessary to vaccinate for chickenpox?

It is very important that all children who are able be vaccinated against varicella. The better the vaccination rate in your community, the smaller the chance that there will be any varicella circulating in your community.

This will provide protection to those who did not respond to the vaccine and to those who cannot be vaccinated. This includes children younger than 1 year of age and people with low immunity either from immune system disease, cancer or medications that suppress the immune system. Older people (older than 60 years of age) can be given a stronger version of this vaccine to boost their immunity to prevent them from developing shingles.

What’s the vaccination schedule?

The first dose is given at 12 to 15 months of age (must be after the first birthday). The second dose is given at 4 to 6 years of age but can be given as soon as 3 months after the first dose.If your child missed one or both doses, he or she should be caught up by giving two doses at least three months apart up to the age of 12 and then two doses at least one month apart starting at age 13. Unvaccinated adults without evidence of immunity to varicella (history of chickenpox confirmed by a physician or born prior to 1980 when virtually all children acquired varicella) should receive two doses of vaccine at least one month apart.

What does the recent study tell us?

The study, sponsored by CDC, was published in the journal Pediatrics (a publication of the American Academy of Pediatrics) describing the impact of two doses of varicella vaccine on the rate of varicella in two communities in the U.S. Monitoring of varicella has been going on in these communities since the introduction of varicella vaccine in 1995.

The researchers found that cases of varicella decreased by a further 67 percent in one community and 76 percent in the other after the recommendation for two doses of vaccine was made.