H1N1 trial results in children show promise

Published in The Hindu on September 22, 2009

Early results from vaccine trials undertaken in 10-17-year-old children show similar results as seen in adults. A majority of the children produced immune response to H1N1 virus in 8-10 days after vaccination. The immune response was seen after just one dose of 15-microgram vaccine. The vaccine used did not contain any adjuvant — a substance added to a vaccine to improve the body’s response.

Very importantly, the vaccine did not cause any serious adverse reaction even in children only a few months old.

Though the immune response seen in children are generally less robust compared to adults, the H1N1 vaccine was able to elicit sufficient immune response to the H1N1 virus in children.

However, the immune response produced by children did vary by age. While 76 per cent of children in the 10-17-age group showed maximum protective immune response, this was 36 per cent in the case of children in the 3-9 age group, and 25 per cent in the 6-35-months age group.

There were 25 participants in the 10-17-years and 3-9 age groups, and 20 in the case of 6-35-months age group.

According to Anthony S. Fauci, Director of the National Institute of Allergy and Infectious Diseases (NIAID), the reducing immune response in children in the lower age group is not totally unexpected. The trend is similar to what is seen with seasonal vaccines, NIAID release noted.

“It is anticipated that the immune response to the 2009 H1N1 influenza vaccine will be similar to that of seasonal influenza vaccination and will continue to rise for several weeks following vaccination,” said Dr. Fauci.

The lower immune response seen in younger children is probably because their immune system is not fully developed. Hence the vaccine is unable to prime the immune system. Most importantly, the immune response may depend on which part of the immune system is activated by the vaccine. Younger children may require a booster dose to increase their immune response.

According to the Centres for Disease Control and Prevention (CDC), Atlanta, children between six months and nine years would require two doses of flu vaccine the first time they get vaccinated.

“If possible, the first [flu] dose should be given as soon as vaccine becomes available. The second [flu] dose should be given 28 or more days after the first dose. The first dose “primes” the immune system; the second dose provides immune protection. Children who only get one [flu] dose but need two doses can have reduced or no protection from a single dose of flu vaccine. Two doses are necessary to protect these children,” notes CDC.

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