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 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.
Don't miss these Health stories
More women opting for preventive mastectomy - but should they be?
- Larry Page's damaged vocal cords: Treatment comes with trade-offs
- Report questioning salt guidelines riles heart experts
- CDC: 2012 was deadliest year for West Nile in US
- What stresses moms most? Themselves, survey says
- More women opting for preventive mastectomy - but should they be?
"It is important to remember that at this time of year we don't normally have influenza," Butler said.
‘Explosion’ in case numbers
On Friday, the World Health Organization warned that the global spread of swine flu will endanger more lives as it speeds up in coming months and governments must boost preparations for a swift response.
Video: Ready for swine flu at work? WHO's Western Pacific director Shin Young-soo predicted there will soon be a period of further global spread of the virus, and most countries may see swine flu cases double every three to four days for several months until peak transmission is reached, said
"At a certain point, there will seem to be an explosion in case numbers," Shin told a symposium of health officials and experts in Beijing. "It is certain there will be more cases and more deaths."
WHO has declared the swine flu strain a pandemic, and it has killed almost 1,800 people worldwide through last week. International attention has focused on how the pandemic is progressing in southern hemisphere countries such as Australia, which are experiencing winter and their flu season.
WHO earlier estimated that as many as 2 billion people could become infected over the next two years — nearly one-third of the world's population.
Separately, in new advice issued to health officials, the WHO said healthy people who catch swine flu don't need antiviral drugs like Tamiflu. Rather than using it to treat healthy people, the drug shouldbe used to treat people in groups at risk for the virus. That includes children less than five years old and people over age 65, among others.
The new advice contradicts government policies such as those in Britain, which has been giving out Tamiflu to all people suspected of having swine flu.
In the U.S., Fauci 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.
Hospitals may be overwhelmed
WHO has stressed that most cases of swine flu are mild and require no treatment, but the fear is that a rash of new infections could overwhelm hospitals and health authorities, especially in poorer countries.
Video: Worries over swine flu vaccine delay Shin said governments must act quickly to educate the public, prepare their health systems to care for severe cases and protect those deemed more vulnerable to prevent unnecessary deaths.
"We only have a short time period to reach the state of preparedness deemed necessary," Shin said. "Communities must be aware before a pandemic strikes as to what they can do to reduce the spread of the virus, and how to obtain early treatment of severe cases."
Pregnant women face a higher risk of complications, and the virus also has more severe effects on people with underlying medical conditions such as asthma, cardiovascular disease, diabetes, autoimmune disorders and diabetes, WHO chief Margaret Chan said in a video address.
The last pandemic — the Hong Kong flu of 1968 — killed about 1 million people. Ordinary flu kills about 250,000 to 500,000 people each year.
Swine flu is also continuing to spread during summer in the northern hemisphere. Normally, flu viruses disappear with warm weather, but swine flu is proving to be resilient.
© 2013 msnbc.com