"Depending on the vaccine manufacturer, the shelf life of the H1N1 vaccines range from 18 weeks to 18 months, with some due to expire on June 30, 2010," Grassley wrote in his letter to Sebelius.
"I understand that it is not uncommon for some seasonal flu vaccines to be discarded each year, but the H1N1 vaccines were paid for with taxpayer dollars," he added, asking: "How many doses of vaccine are due to expire on June 30, 2010?"
Hall said the department would respond to Grassley.
"There are approximately 71 million doses, held by states, the distributor or the manufacturers, that remain unused, and have varying expiration dates, some as long as early 2011," Hall said by e-mail.
"We have asked states to hold on to any vaccine that has not expired, in case we continue to have regional upticks in disease, another wave, or another early start to the flu season. We are holding onto that vaccine (and advising states and vaccinators to hold onto theirs) until there is sufficient seasonal vaccine (which includes coverage for the 2009 H1N1 virus) to replace it."