The drug, tested on 500 people in Australia, triggered an immune response against all four viral strains after 21 days.

It also showed promising signs of meeting the U.S. Food and Drug Administration's eligibility criteria to gain an "accelerated approval."

The FDA grants accelerated approval to drugs that target an unmet medical need, or ones that are advantageous over current treatments, by expediting the review process.

Novavax said it is "evaluating both process and assay refinements" that it believes will further improve immune responses of its vaccine.

This would push the start of the next mid-stage trial of the experimental vaccine to 2013, rather than the fourth quarter of this year, Chief Executive Stanley Erck said in a statement.

The company's shares closed at $1.72 on Tuesday on the Nasdaq.

(Reporting by Zeba Siddiqui in Bangalore; Editing by Roshni Menon)

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