"I don't think there's a smoking gun and I want to make that really clear. It is a very complicated process," Health and Human Services Assistant Secretary for Preparedness and Response Nicole Lurie said at the House Energy and Commerce Oversight Subcommittee hearing.
"I don't think there's anybody to blame here," Lurie said.
But Rep. Greg Walden, R-Ore., who was out of work in late October after being diagnosed with H1N1, did not seem satisfied with the response, probing further about the HHS Secretary Kathleen Sebelius' awareness of vaccine delays when testifying in September.
"We had testimonies September 15 from Secretary Sebelius and everything seemed to be on track and fine. So, explain who, did the manufacturers, weren't they straight with you? What's this rosy picture piece?" Walden pressed.
"At every step of the way things happened," said Laurie. "When the secretary testified she was using the best available information she had at the time."
Health officials also appeared on Capitol Hill Tuesday before the Senate Homeland Security and Governmental Affairs Committee. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases, conceded during her testimony that the government was partially at fault for leading Americans to expect more H1N1 flu vaccine than would be ultimately available.
"One thing I think we can look back and say was a mistake is some of our communication… whether we meant to or not, I think we led expectations of availability to be higher than they have been, and so that, that I think can lead to frustration," Schuchat testified.
Sen. Susan Collins, R-Maine, the ranking Republican on the committee, highlighted the anxiety expressed by her constituents, citing an 11-year-old boy who fell into the "high-risk" category, but still had difficulty getting vaccinated.
"He has two auto-immune diseases and asthma, placing him in the high-risk group for complications. Yet even after his mother called several possible sources, schools, the main CDC, doctors' offices both in Maine and in Boston, hospitals, health care clinics, pharmacies, she could not find any vaccine available for her son."
Collins said a source was eventually found nearly a six-hour roundtrip drive from the family's home.
"That," she said, "is just not right." Collins reminded Schuchat that her boss Sebelius painted a much brighter picture of the vaccine plan over the summer.
"Secretary Sebelius said by early November, 'We are confident that vaccine is going to be far more widely available. There is enough vaccine and will be to vaccinate every American who wants to be vaccinated and we are pushing it out as quickly as we can,'" Collins said.
Earlier this week, Collins and Sen. Joe Lieberman, I-Conn., who chaired the hearing, had written a letter to Sebelius, demanding to know why the HHS department "insisted on promoting a plan for which the federal government did not have anywhere near sufficient resources to implement."
High-risk Groups Left Scrambling, Senators Say
"The glaring discrepancy between the demand for and supply of H1N1 vaccine in our country has resulted in pregnant women standing in line for hours, only to find no vaccine at the end," the Nov. 16 letter said. "This shortage of vaccine has left many parents of children in high-risk groups scrambling, often in frustration, to find the vaccine the government has told them that they need."
"I hate that people had to wait in line, or that people haven't been able to find vaccine, but our surveys tell us that those who looked for vaccine and were unable to get it, nine out of 10 plan to look again," Schuchat said Tuesday.
"Fortunately, it is getting a little bit easier each day, although not yet at the point where demand and supply have gotten close enough together," she said.
Witnesses Tuesday attributed the vaccine shortage to initial uncertainty in public demand for the vaccine, manufacturing and shipping problems, including bad weather, and the slow-growing nature of the virus in manufacturing the vaccine.
"I share your disappointment in the initial production and the set of supply constraints we have today," Schuchat said. "But production is accelerating; substantial amounts are becoming available, not as much as we want, but more every day. Today 48.5 million doses of H1N1 vaccines are available for the states to order."
Laurie told the panel Tuesday that delays were also caused, in part, by poor production yields and decisions in the home country of the manufacturer.
"While the delays are really frustrating to everybody," Laurie said, "it is really the virus that is the real enemy here."
According to figures released by the CDC last week, since April an estimated 22 million people in the U.S. have become ill from the H1N1 virus, 98,000 people have been hospitalized, and 3,900 people have died, including 540 children.
Two Separate Lists for Vaccine Recipients Confused Public, Lieberman Says
Lieberman blamed part of the public's frustration on the CDC creating two separate lists of individuals who should receive the vaccine first -- a broad "high-priority" group of 160 million people, and an alternate "most at-risk" group of 42 million people if supplies should fall short.
"That's what's caused the public outrage, basically, that the initial description of 160 million people who were eligible -- not just eligible, but 'at-risk,' and then ending up with now, finally 42 million," Lieberman said, adding the separate lists hurt states' ability to prioritize who should get vaccinated first.
Schuchat said a CDC advisory committee for immunization practices had advised the CDC to let state and local governments decide how to distribute the vaccine.
"What we heard pretty consistently was, 'leave the flexibility to the states and locals. Let them decide whether to sub-prioritize,'" Schuchat explained.
The CDC's broader priority list included pregnant women and recently pregnant women, caretakers of children younger than 6 months, health care and emergency medical services personnel, people aged 6 months through 24 years, and persons aged 25 through 64 years who have health conditions associated with higher risk of medical complications from influenza, such as asthma or heart disease.
The smaller list, according to the CDC, included pregnant women, caregivers of children younger than 6 months of age, health care and emergency medical services personnel, children aged 6 months to 4 years, and children aged 5 to 18 who have higher risk of medical complications from influenza.
A recent Harvard School of Public Health poll found that a majority of adults who tried to get the H1N1 vaccine for themselves or their children were unable to do so. The poll, conducted Oct. 31 to Nov. 1, found that since the H1N1 flu vaccine became available in October, 17 percent of American adults, 41 percent of parents, and 21 percent of high-priority adults have tried to get it.
91 Percent Who Failed to Find the Vaccine Will Go Again, Survey Finds
Among the adults who tried to get it for themselves, 70 percent were unable to get the vaccine; among the parents who tried to get the vaccine for their children, 66 percent were unable to do so; and of the high-priority adults, 66 percent were unable to get it, according to the poll.
The poll also found that nearly a third of those who have tried and could not get the vaccine, either for themselves or for their children, are very frustrated. However, the poll also said 91 percent of those who have tried and not been able to get it yet will try again this year to get the vaccine for themselves, their children or both.
ABC News' Lindsey Ellerson contributed to this report.