Weak shield
vaccination against chickenpox has been popular in the us for nearly a decade. But outbreaks of the illness among children already immunised have raised concerns about the effectiveness of the vaccine. Now a new study intensifies the debate. Researchers from the us-based Yale Medical School report that the effectiveness of the vaccine fades substantially a year after its administration. The vaccine also appears to confer less immunity to children vaccinated before they are 15 months old.
During the study, the researchers analysed 339 vaccinated children who had chickenpox and compared them with 678 immunised children who did not suffer from the disease. A year after the vaccine was given, its effectiveness was found to wane among all the children, slipping from 97 per cent (when the kids were two years old) to 84 per cent (when they were eight years old). For children who were given the shot when they were 15 months or more, the protection level was 99 per cent in the first year of being immunised. But in children who were vaccinated before 15 months of age, the immunity level during the first year was only 73 per cent.
The findings, published in the Journal of the American Medical Association (Vol 291, No 7, February 25, 2004), highlight an acute problem, assert some experts. An ideal solution, they opine, is to combine the chickenpox vaccine with the measles, mumps and rubella vaccine, which is known as mmr. This would enable children to receive a second, or booster, dose of the chickenpox vaccine, because mmr is administered twice.