States and other providers should hang on to the vaccine and continue to offer them to people until drug companies can start distributing seasonal vaccine for the coming influenza season in the autumn, said Health and Human Services Department spokesman Bill Hall.
Senator Chuck Grassley, the ranking Republican on the Senate Finance committee, released a letter on Monday that he sent to HHS Secretary Kathleen Sebelius asking her how much vaccine was left over and when it would expire.
H1N1 swine flu is still technically causing a pandemic and health officials say anyone who has not been vaccinated should still try, in case it causes a third wave of serious disease.
Health experts consider swine flu likely to join the mix of seasonal flu viruses and it will be included in the seasonal flu vaccine for 2010-2011, which will also contain two other flu strains.
When the H1N1 virus started spreading in April, HHS and its agencies, along with commercial flu vaccine makers, rushed to formulate and make a vaccine.
Vaccine started rolling out in October and the U.S. eventually ordered 229 million doses from its five licensed makers - Novartis, AstraZeneca unit MedImmune, Sanofi Aventis, GlaxoSmithKline and Australian vaccine maker CSL.
Sebelius said last month that 162 million doses were produced and distributed, but only 90 million actually got into people's arms or noses.
VARYING SHELF LIFE
"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."
The U.S. Centers for Disease Control and Prevention estimates that H1N1 has killed at least 12,000 Americans and put more than 265,000 in hospital. People with chronic diseases such as asthma or diabetes, pregnant women and children were at highest risk.
Grassley also asked Sebelius whether HHS would try to increase distribution of seasonal flu vaccines.