There have been no serious side effects from the first set of injections of the new swine flu vaccine, federal health officials have said in predicting that nearly 200 million doses could be produced by years end.

Clinical trials in adults began on August 7, and those in children on Wednesday.

There are no red flags regarding safety, said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, which is overseeing the trials.

Because the only side effects in adults were sore arms, which are typical of any flu shot, trials on children were able to begin, and those in pregnant women are expected to begin early next month, Dr. Fauci said in a telephone news conference with officials from the Food and Drug Administration and the Centers for Disease Control and Prevention.

The vaccine will be tested in about 4,500 people. That is far too few to pick up subtle side effects, but the virus strain in the vaccine is close enough to one strain in seasonal shots so that side effects are expected to be similar.

The trials will help officials decide whether to recommend one dose or two. Even with seasonal flu shots, young children who have never had the flu sometimes need two doses to get a take vaccinologist jargon for a protective immune response.

Unless the virus changes, health officials do not expect to recommend mixing in adjuvants. Adjuvants, usually oil-water emulsions or aluminium salts, boost the immune system but also often heighten unpleasant side effects.

Since it was first detected in April, the pandemic virus has not produced any nasty new surprises during its spread around the world, said Dr. Jay C. Butler, director of the A(H1N1) Vaccine Task Force at the CDC.

Flu activity in the Southern Hemisphere, which soared in June at the beginning of its winter, has begun to wane. The virus has not crossbred with other flu viruses or mutated to produce proteins that could make it more lethal. And while some Tamiflu-resistant virus has been found in several countries, it has not become widespread.

2009 The New York Times News Service trials on children were able to begin; virus has not crossbred with other flu viruses

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