US regulators stole a march on their European counterparts on Tuesday by approving four pandemic flu vaccines, clearing the way for an immunisation programme to begin across the country next month.

The Food and Drug Administration said it had authorised the use of products made by CSL, Sanofi-Aventis, Novartis and MedImmune, using the traditional techniques for seasonal flu but adapted to help protect against the current H1N1 swine flu virus.