Varicella Vaccine Less Effective over a Period of Time

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Varicella Vaccine Less Effective over a Period of Time

Posted on : Thu, 15 Mar 2007 08:41:01 GMT | Author : Goodyear

If you had chickenpox, also known as varicella zoster, as a child, the

chances of you contracting the disease again as an adult are not as remote

as you would think, even if you have been vaccinated against it.

Recent studies reveal that Varivax, the vaccine manufactured by Merck,

against chickenpox tends to grow less and less effective over a period of

time. The studies suggest that a second dose should be administered to

protect against a more severe case of the disease long term.

These findings were reported on Thursday in the New England Journal of

Medicine by Chaves leader of the research team from the Center for

Disease Control and Prevention in Atlanta, and Jane Seward, acting deputy

director of the CDC's division of viral diseases.

This confirms what doctors were already aware of - that the vaccine did not

protect one against the disease for a long time.

The report also suggests that besides losing its effectiveness the vaccine

has also changed the disease profile.

The number of children who had been vaccinated and yet contracted chicken

pox increased with each successive year. This again suggested that the

protection was not complete and permanent.

Again, the study showed that children who had been vaccinated and yet

contracted the disease at an older age in spite of it tended to be sicker.

It has been confirmed that as children who were not vaccinated or children

in whom the first dose was ineffective, mature into adults, they tend to

contact the disease as they mature. This is more dangerous due to the risk

of severe complications being higher in adults.

The chances of an adult who has contracted chicken pox having to be

hospitalized is about fifteen times more than for a child. He or she is also

about twenty times more at risk of dying from the disease.

It was also found that the number of children who had been vaccinated and

yet contracted chicken pox increased with each successive year. This again

suggested that the protection was not complete or permanent.

As a result of these findings the CDC's Advisory Committee on Immunization

Practices has now recommended a booster shot be administered to children

between the ages of four and six. In a previous report in June, 2006 it had

also recommended that everyone be given booster shots regardless of age.

Another vaccine also made by Merck, Zostavax,a booster for adults had been

approved in May, 2006.

How effective or how long lasting the effects of the second shots will be

are yet to be seen according to Chaves. The researchers are hoping that the

booster shots will increase the efficiency of the vaccine to 90%.

Children have been vaccinated against chickenpox since 1995. However

investigations revealed that the vaccine is effective only in 80% to 85% of

these cases.

The research team studied ten years of collected data about the disease in

350,000 people, in Antelope Valley, California.

However the study's findings do find that the vaccine is partially

effective. During the surveillance period only 10% of the 11,356 people who

contacted chicken pox had been vaccinated against it once. This suggests a

certain amount of protection against varicella.

The chicken pox virus lingers in the body for a person's lifetime and can be

triggered once more, resulting in a painful rash known as shingles.

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