Weakening, spray for swine flu recalled

The vaccine recall is the second this month caused by declining potency and comes as public health officials urge millions of Americans to get vaccinated against swine flu.

The action affects more than 4.6 million doses, but the vast majority have already been used, according to the Food and Drug Administration. Agency officials said the vaccine was strong enough when it was distributed in October and November.

“The slight decrease in potency is not expected to have any effect on the protective effect of the vaccine,’’ said Norman Baylor, director of the FDA’s vaccine research office. “We are not recommending revaccination.’’

The agency is looking into the problem but said it is not uncommon for vaccines to lose strength over time. MedImmune’s vaccine has a recommended shelf life of about four months.

Last week, vaccine maker Sanofi Pasteur recalled hundreds of thousands of swine flu shots for children because tests indicated those doses lost some strength. Most of those doses had already been used, too.

Swine flu vaccine has been available since early October, and manufacturers have released more than 111 million doses for distribution in the United States.

Maryland-based MedImmune makes the only nasal spray version, which can be used by healthy people ages 2 to 49.

“It’s not a safety concern. People who have received doses from the affected lots do not need to be revaccinated. The doses were well within potency specification,’’ said spokesman Tor Constantino.

Only in recent weeks have state authorities lifted restrictions on who can get vaccinated. Previously the vaccines were reserved for high-risk patients, including pregnant women and schoolchildren.

Dr. Anne Schuchat of the federal Centers for Disease Control and Prevention estimated that 60 million Americans have received swine flu vaccine and said intense monitoring for side effects has not turned up any concerns.

“We are not seeing any worrisome signs,’’ she said.