UPDATE 1-AstraZeneca gets $90 million U.S. flu vaccine order

* Order for nasal spray vaccine against H1N1 flu

* Company sees potential for additional U.S. orders

(Adds detail, background)

LONDON, June 1 (Reuters) - AstraZeneca's (AZN.L) MedImmune biotechnology unit has won an initial $90 million order from the U.S. government to make a live attentuated vaccine against the new H1N1 flu strain, it said on Monday.

The potential exists for further additional orders from the U.S. Department of Health and Human Services (HHS), it said.

MedImmune's vaccine technology, currently only available in the United States, is different from traditional injectable flu shots in that it is a mist sprayed into the nose, where the flu virus usually enters the body.

It contains live, weakened virus that does not cause the flu but still prompts the body to mount an immune response.

The HHS said on May 22 it was setting aside $1 billion to help companies develop vaccines against the new strain of H1N1 influenza sweeping the world.

Experts say a vaccine against the new strain -- also known as swine flu -- would probably have to be given separately from the seasonal flu vaccine, which is a mixture of three flu strains reformulated every year. Vaccine makers are almost done with making the autumn flu vaccine for the northern hemisphere.

MedImmune plans to begin shipping the first of 10 million doses of its seasonal FluMist vaccine to U.S. healthcare providers in August. (Reporting by Ben Hirschler; Editing by Dan Lalor)