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 Sandra 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.
