- The Washington Times - Tuesday, September 22, 2009

Healthy children age 10 and older most likely will need only one shot for protection against this year’s new flu strain, H1N1, while younger children will require two doses - the usual for seasonal flu.

The recommendations were announced Monday after studies of the latest vaccine done since mid-August by the National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health.

In another bit of good news on the H1N1 vaccine development, Dr. Anthony Fauci, NIAID director, said effective protection began eight to 10 days after youths ages 10 to 17 received the 15-microgram dose. The shot builds up the body’s immune system incrementally immediately after a shot, though it takes more than one week of that process for the person to be considered resistant.

The dose was less effective in younger children, thus two doses will be required for that group - ideally, to be given 21 days apart.

“This is similar to what we see in seasonal flu vaccine,” Dr. Fauci said. “Overall, this is very good news for the vaccination program, both for its supply and potential efficacy.”

The trial of the dosages being manufactured by Sanofi-Aventis SA, one of five manufacturers developing H1N1 vaccine, involved about 600 children.

The study also found that a 30-microgram dose of the vaccine did not work significantly better than the 15-microgram dose.

Manufacturers are considering an even smaller dose for toddlers between 6 months and 35 months, Dr. Fauci said.

Authorities are not recommending the vaccine be given to infants 6 months or younger because the lack of a mature immune system at that age means vaccination doesn’t help. Children younger than 10 will need two doses because they would not have enough immunity from prior exposure to either vaccines or viruses.

Thus, children younger than 10 generally will need four shots - two for the regular seasonal or winter flu, and two for the H1N1 strain, commonly called swine flu.

“The older you get, you may have some immunity - the young not as good as adults, but they may have some prior exposure,” Dr. Fauci said. “The presumption is that older individuals over years of experience have come into contact with a virus that may have some slightly overlapping identity with the current one. Children haven’t lived long enough to have this. Their immune system isn’t primed as well to be receptive to the virus because they probably haven’t seen any version of it.”

Once the new vaccine starts arriving next month, people of any age will be able to get a seasonal flu shot and an H1N1 shot in each arm on the same day, said Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention (CDC).

“What pediatricians should be telling parents now is what both the CDC and [Health and Human Services] and others are saying: Get the seasonal flu vaccine now and the H1N1 later” when it arrives on the market, Dr. Fauci said.

“We think this will be a complicated flu season, which is why we are working so hard,” Dr. Schuchat said.

The results echo a report issued last week by vaccine-maker GlaxoSmithKline PLC that a single dose of the H1N1 vaccine would be enough to protect most adults after 21 days.

Early results in another study done by the Australian company CSL Ltd. show similar outcomes. Adults ages 18 to 24 - a target group for the new pandemic virus - were given a 15- and a 30-microgram dose and both proved equally effective. All the vaccines tested appeared to be safe in preliminary tests.

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