But Dr. Anne Schuchat, the director of the National Center for Immunization and Respiratory Diseases, said the estimate gives a "more accurate picture" of the scale of the pandemic.

CNN: H1N1 death toll estimated at 3,900 in U.S.

But due to manufacturing delays, "we think at most it will be 10 to 12 million doses less, " said Dr. Anne Schuchat, CDC's director of the National Center for Immunization and Respiratory Diseases.

CNN: CDC: Production of H1N1 flu vaccine lagging

In January 2011, President Barack Obama signed the Zadroga Act, named after New York Police Detective James Zadroga, who died of a respiratory illness after working at the World Trade Center site.

CNN: 9/11 responders wait for compensation for their illnesses

Firefighters who raced to the World Trade Center collapse last month will be checked for respiratory problems.

CNN: Recovery: Aviation security debate continues

Beth Israel Medical Center in Manhattan received about 100 patients with injuries ranging from respiratory stress and minor injuries.

CNN: Rescuers: Expect thousands dead