US health officials announced on Tuesday that nearly 5 million doses of a nasal spray version of swine flu vaccine have been recalled because the vaccine loses potency over time, although not enough to diminish its protective effect.

Specifically, 4.6 million doses of vaccine produced by drug maker MedImmune were involved in the recall. Most of the doses have already been used, and was strong enough when it was distributed in October and November.

FDA spokeswoman Pat El-Hinnawy said the action was a “voluntary, non-safety related recall. There are no safety concerns about the vaccine. The decrease in potency is not likely to be clinically significant. Individuals who received doses from the recalled lots do not need to be revaccinated.”

The vaccine by manufacturer Sanofi Pasteur was also recalled when about 800,000 children’s doses of injectable H1N1 swine flu vaccine showed loss of protective effect.

(via Yahoo News)