The US Food and Drug Administration on Tuesday approved a vaccine designed to protect against swine flu and hopes to make it available within a month.

The regulator approved the vaccine manufactured by four different pharmaceutical companies and said the first batches of shots should be available within the next four weeks in the US.

The H1N1 vaccine produces immunity within eight to 10 days of the injection.

The first major outbreak of the new variant of the influenza virus occurred this spring in Mexico and quickly spread across the world.