Some 12 million doses of H1N1 flu vaccine will expire by Feb. 15. That is earlier than expected, according to manufacturer Sanofi Pasteur, which recently notified U.S. governmental agencies of this finding.

The shelf life is being shortened because the doses are losing their potency more rapidly than expected. There are no safety concerns with these doses. The 50 lots subject to the change in expiration date contain prefilled syringes and exclude multi-dose vials.The lots were shipped to providers between November 2009 and January 2010, according to an update from the Centers for Disease Control and Prevention.

Sanofi Pasteur plans to send a notification to providers that preeived doses from any of the 50 lots.