Vaccine maker MedImmune has voluntarily recalled 13 lots of vaccine against the pandemic H1N1 influenza because they have lost some potency since they were manufactured, the company said. The 13 lots recalled involved 4.7 million doses of the intranasal vaccine, which is based on a live, weakened virus, but officials believe most of them were administered in October and November when the product would have still been at full potency. The company still has 3,000 doses of the vaccine affected by the recall, but no one knows how many are in warehouses around the country. This is the second recall of a swine flu vaccine. Just a week ago, Sanofi-Aventis recalled 800,000 doses of vaccine for children because it too had lost some potency.