Around the world pharmaceutical companies have been producing vaccine strains for at least a month. Some are in the experimental stages, while others are approaching the need for clinical trials. However they are "by no means" ready yet, according to the World Health Organisation.

The Department of Health has said it has signed contracts to supply enough vaccines for the entire population in the UK and expects the first batches to arrive in the early autumn.

In April, the race to produce a successful vaccine against H1N1 began in earnest when, under orders from the WHO, institutes in the UK, the US, Japan and Australia began work to produce a "seed strain" of the virus, which could then go on to produce a vaccine.

In the UK, scientists at the Health Protection Agency's National Institute for Biological Standards and Control (NIBSC) in Potters Bar, Hertfordshire, began work on a strain isolated from a patient in the US. Using a technique called reverse genetics, the scientists took the genes that make the outer coating of the swine flu virus and then attached them to a harmless human virus known as PR8.

This reconstructed virus is considered safe for humans and will trigger an immune response that protects people against the swine flu strain.

By 28 May, NIBSC had completed its work. It sent the starter virus out to manufacturers including GSK and Baxter.

The next step was to develop the virus and grow it inside chicken eggs, to produce it in vast quantities. The production involves refining it further and then, once the experimental phase is finished, conducting clinical trials of the vaccine.

It has been reported that CSL, a biopharmaceutical firm, has created an effective vaccine in a Melbourne laboratory, but it is awaiting human trials.

Yesterday, a spokesman for GSK said the company expected its "final vaccine" to be available in the autumn. "We have started production. We are talking to the different health authorities and the governments around the world to find out what level of clinical trials will be required, for instance, how long, [and] how many people would be involved."

Commenting on when vaccines would be ready for use, Marie-Paule Kieny, director of the Initiative for Vaccine Research at the World Health Organisation in Geneva said: "They are produced but they are by no means ready to be licensed yet."