Clinical trials for the new swine flu vaccine have turned up no red flags, U.S. health officials said on Friday.

The first results from studies of the new vaccines in adults and the elderly will be available in mid-September, but so far, the only complaints seem to be a bit of local soreness and redness in the arm at the injection site, they said.

There are no red flags regarding safety, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, one of the National Institutes of Health.

Fauci said no side effects were seen 10 to 14 days after the first studies in adults, giving health officials the confidence to start trials of the vaccines in children this week.

There is no sign yet of whether the new vaccines will produce enough of an immune response to protect people against the new pandemic H1N1 flu.

Two trials are underway in adults for the safety and effectiveness of two doses of the vaccine. The trials, which are also looking at whether one or two vaccinations will be needed, are nearly fully enrolled.

We expect first dose data somewhere around mid-September if all goes well, and second dose data by mid-October, Fauci said in a telephone news briefing.

He said first dose data from the trial in children will be available in late September, and second dose data will be ready in late October.

Fauci said studies in pregnant women should begin in early September, as will studies using an immune system booster called an adjuvant. In all, the vaccines will be tested on nearly 4,600 people.

The U.S. Centers for Disease Control and Prevention said swine flu is still spreading widely across the United States, with 75 percent of serious cases and 60 percent of deaths among people under the age of 49. Alaska and Maine had widespread activity.

CDC has officially confirmed 7,963 hospitalizations and 522 deaths from the pandemic H1N1 flu, said CDC's Dr. Jay Butler. He said there were likely more than a million actual cases, as most patients never get tested.

It is important to remember that at this time of year we don't normally have influenza, Butler said.

He said the government expected to have 45 million to 52 million swine flu vaccine doses by mid October, when vaccination is expected to begin, and 195 million by the end of the year.

Fauci said even after people are vaccinated they should be aware they are not immediately protected -- the immune response from a vaccine takes about two weeks to develop.

Five companies are making both seasonal and H1N1 flu vaccines for the U.S. market -- AstraZeneca's MedImmune unit, CSL, GlaxoSmithKline Plc, Novartis AG and Sanofi-Aventis SA.

Fauci said he expects an upsurge of flu cases in the autumn, as weather cools and students return to school. U.S. government officials have urged schools and businesses to encourage people to stay home when they are sick, to wash their hands frequently and keep workspaces clean.

Butler said reports from Chile that turkeys have become infected with H1N1 virus are not a surprise. Because of the swine characteristics of this virus, it can have the capacity to infect turkeys, he said.