The announcement came a day after Novartis said it expected a vaccine for the virus, the source of the first flu pandemic in 40 years, to be available by September.

The Baxter and Novartis vaccines were both developed using cell-based technology that could allow for much more rapid production and distribution than traditional vaccines produced using chicken eggs.

The Novartis vaccine will enter clinical trials next month, the Swiss drugmaker said last Friday, a day after the World Health Organisation (WHO) declared a pandemic and warned governments to prepare for a long battle against the virus.

Baxter said it has completed testing and evaluation of the virus and would submit its H1N1 flu vaccine for approval upon completion of initial manufacturing runs.

European drugmakers Novartis, Sanofi-Aventis, GlaxoSmithKline (GSK) and Solvay all obtained the H1N1 flu seed virus in recent weeks and aim to have a vaccine ready ahead of the flu season in the northern hemisphere.

The WHO has estimated vaccine-makers could produce up to 4.9 billion pandemic flu shots a year in a best-case scenario, leaving some of the world's 6.5 billion population unprotected, particularly if more than one injection was needed to gain immunity.

Novartis said first results with the H1N1 wild type strain showed it was quicker to make the vaccine through cell-based rather than through egg-based production, and it had completed its first batch weeks earlier than expected.

Its cell-culture vaccine plant in Marburg, Germany, had the potential to produce millions of doses a week, but it was difficult to predict output capacity for now.

Spokesman Eric Althoff said Novartis should have the vaccine ready in September or October. He was unsure if other companies had completed the first stage of the production process. -- REUTERS