0 * Flu vaccine development on track, WHO says
* First clinical trial results and approvals in Sept
* Vaccine yields higher after initial problems
(Adds further quotes, details, background)
By Jonathan Lynn and Ben Hirschler
GENEVA/LONDON, Aug 6 (Reuters) - The first vaccines to combat H1N1 swine flu should be approved and ready for use in some countries from September, the World Health Organisation said on Thursday.
Marie-Paule Kieny, WHO director of the Initiative for Vaccine Research, also said vaccine production yields were improving, following a disappointing start that triggered some worries about supplies.
One of the virus strains used by vaccine makers now seems to be yielding the same amount as seasonal vaccine, while early indications were that pandemic H1N1 yields might be only 30 percent of normal.
"I don't want to say too early that the question has been resolved but it really seems that we have found a way to go round this problem," Kieny told reporters. "We are on track in development."
First results from clinical trials are expected early next month and these tests will show whether one or two doses are needed to provide immunity -- another big swing factor in determining how many people can be vaccinated.
Once initial clinical trial results are in, regulators will be able to approve the vaccines from next month and the first countries are expected to start mass vaccination programmes, Kieny added.
The H1N1 flu outbreak, declared a pandemic on June 11, has spread around the world and could eventually affect 2 billion people, according to WHO estimates.
Fears the strain could become resistant to the anti-viral drug Tamiflu have underscored the need to get vaccines to market quickly. The H1N1 vaccines would be given separately from regular seasonal flu shots.
Leading flu vaccine makers include Sanofi-Aventis, GlaxoSmithKline, Novartis, Baxter, CSL and Solvay.
WHO Director-General Margaret Chan has said the H1N1 virus is stable and there were no signs of it mixing with other more dangerous types of influenza such as the deadly H5N1 bird flu strain.
At present, patients with mild symptoms generally do not need any medicines to recover, and Chan has stressed hospital visits are not necessary unless those infected with flu have certain warning signs.
These include long-lasting high fever in adults and a lack of alertness in children. Pregnant women and people with health problems including diabetes are also vulnerable to more severe effects from the new flu strain.
FAST-TRACK APPROVAL 'SAFE'
The WHO said vaccines had to be available quickly and in large quantities to have the greatest impact and it insists that fast-track approval will not jeopardise safety.
Vaccines arrived too late in the 1957 and 1968 flu pandemics to be of much use, and flu vaccines had not been developed in the 1918 "Spanish flu" pandemic which killed an estimated 50 million people.
Some concerns have been raised because of serious side effects and 30 deaths seen during a U.S. swine flu vaccination in 1976.
Kieny said vaccine production and purity levels had improved significantly since but safety issues could arise during a pandemic when a vaccine is administered on a mass scale, even if they did not show up in safety trials.
As a result, countries are being advised to conduct intensive monitoring as the vaccination campaign goes on.
(Additional reporting by Laura MacInnis; editing by Michael Roddy)