AstraZeneca P.L.C.'s MedImmune unit announced a recall of 4.7 million doses of its nasal spray version of the swine flu vaccine because tests showed a decline in potency, U.S. regulators said yesterday.

There are no questions about the safety of the doses, and people who have already been inoculated don't need to get vaccinated again, said Norman Baylor, director of vaccines research and review for the Food and Drug Administration. About 3,000 of the doses remain in warehouses, and AstraZeneca will contact clinics that may still have unused vials, he said. The company has its U.S. headquarters near Wilmington.

The recall follows a similar move on Dec. 15 by Sanofi-Aventis SA, which recalled 800,000 doses of swine flu vaccine. After vaccines are shipped from the manufacturers, companies keep samples from each lot and continue to test them for potency declines, Baylor said. Both swine flu vaccine recalls were voluntary after potency dropped below pre-specified thresholds.

"There are no safety concerns with these lots," Baylor said in a conference call with reporters yesterday. "We do see a decline in potency every now and then."