In 2000 the CDC and US goverment introduced a vaccine for chickenpox. The vaccine was recommended for all children after the age of 12 months. It was introduced as a single vaccine, not requiring a booster, based on preliminary trials. But a new report published this month in Pediatrics states that outbreaks of chickenpox among vaccinated children is still high. The authors are suggesting that a booster may be needed.
Varicella zoster, the virus that causes chickenpox is spread via direct contact with sores. It can also be spread via blood. Most children will contract chickenpox by the age of 10 years, either from someone at school or a "chickenpox party". Because varicella is a herpes virus, it lives dormant in the nerve cells and can become activated in adulthood, causing a condition know as shingles.
Adults who have not had a primary outbreak of chickenpox in childhood can devleop adult chickenpox. In this group the disease can be very severe, causing hospitalization in some cases. In a child the disease is less severe and the greatest concern is having the child home from school for 2-3 weeks in some cases and the parents missing work during that time. There is no treatment for chickenpox, only symptomatic relief. Women who are pregnant and have never had chickenpox need to be extra precautious when an outbreak occurs because the virus can spread to the newborn.
The vaccine was introduced with the expectation that chickenpox outbreaks and total numbers of children with the disease would decrease. The new report seems to object to that idea. For the study one particular outbreak in an elementary school in Arkansas was studied. A total of 545 children who had never had chickenpox attended the school, 96% of whom were vaccinated against varicella. A total of 48 students contracted chickenpox during the outbreak. 90% of those who developed chickenpox had been vaccinated against varicella.
These results were quite surprising, given the preliminary trials of the vaccine. The children who had been vaccinated reported a more mild case of chickenpox than children who had not been vaccinated. Overall effectiveness of the vaccine based on this population was 82%, and 97% for preventing severe cases.
Given the low effectiveness of one injection, the authors conclude that a second booster dose may be able to increase protection. For many of the vaccines, more than one injection is required to reach 95% effectiveness. Each injection causes a small immune response that is cumulative to previous exposure or vaccine. The only way to have 100% protection against development of any disease is to contract the condition naturally.
Reference
1. Pediatrics June 2006.
Posted by Dr. Christina Gutierrez on June 23, 2006 01:40 PM
