A child is restrained as he receives the H1N1 vaccine in nasal spray form… (Tim Sloan / AFP/Getty Images )
Vaccine manufacturer Sanofi-Aventis is recalling 800,000 doses of H1N1 vaccine meant for children younger than 3 because the influenza vaccine has lost potency since it was shipped from the factory.
"This is non-safety-related, but is part of a routine quality assurance program," Dr. Anne Schuchat, director of the Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, said in a telephone interview Tuesday.
There are now 94.6 million doses of vaccine available, "so this is not as big a deal as it might have been earlier," she said.
She emphasized that "there are no safety concerns."
The doses in the recall are pre-filled syringes containing thimerosal-free vaccine made specifically for children ages 6 months to 35 months.
At the time of the vaccine's manufacture, testing showed that the doses contained the recommended 7.5 micrograms of antigen, the virus component that is used to stimulate immunity.
But later testing of one lot of the vaccine showed that some of the antigen had apparently degraded slightly, leaving the vaccine less potent than desired.
Follow-up tests identified three other lots with the problem, bringing the total to four lots comprising 800,000 doses. It is not highly unusual for stored vaccines to undergo some degradation, but it is not yet known why that happened in this case, Schuchat said. It doesn't appear to be a storage issue.
Sanofi is one of five vaccine manufacturers whose products are approved in the United States. All of them routinely check their products for potency at regular intervals; none of the others have reported problems.
Children who received the vaccine do not need to be re-immunized, Schuchat said, because they probably received a sufficient dose, "but we wanted to make sure that doses that weren't already given won't be."
She emphasized that children who have received only one dose of vaccine should get their scheduled second dose. Two doses are required to provoke full immunity in children younger than 10, as is the case with seasonal flu vaccine.
In adults and teens who have received flu vaccinations in the past, the body retains some residual immunity to flu viruses. But for young children who have never been vaccinated, the first dose provides only partial immunity and a second dose is required for full protection.