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 yesterday.

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.

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, Ms Kieny added.

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 per cent 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 get around this problem," Ms Kieny told reporters. "We are on track in development."

The Sunday Times last Sunday reported that the local authorities have decided not to compromise vaccine safety, preferring to wait for a fully-tested jab expected to be available towards the beginning of next year.