U.S. public health officials defended the distribution of swine flu vaccines on Tuesday against criticism that their plan to protect Americans was confusing and over-optimistic.

As of Monday, manufacturers had delivered 48.5 million doses of H1N1 vaccine, Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention told a Senate hearing. HHS had hoped to have as many as 120 million doses by now.

In September HHS Secretary Kathleen Sebelius had assured Congress, “There will be enough vaccines for everyone.”

The problem was worsened because the first vaccine to be available was a nasal spray made by AstraZeneca

unit MedImmune that is not suitable for some of the most vulnerable groups but which is perfect for most schoolchildren and healthcare workers, officials said.

Members of the Senate Homeland Security and Governmental Affairs Committee pressed for an apology and said they felt President Barack Obama’s administration had not learned some valuable lessons from the continuing problem.

“I am worried that we are undermining confidence in our public health system,” said committee chairman, Connecticut independent Sen. Joseph Lieberman.

He worried that people who have waited in vain to be vaccinated against H1N1 swine flu will stop trying.

“This hearing is critical to peeling away the layers of misinformation and miscommunication that has hampered the federal government’s pandemic influenza strategy,” added Maine Republican Senator Susan Collins.

The U.S. government is struggling to vaccinate as many people as possible against the virus, which has infected an estimated 22 million Americans and killed 3,900.

Schuchat acknowledged over-promising vaccine.

“We led expectations of availability to be higher than they have been. I think that led to frustration,” she said.

REVISING DOWNWARD

The vaccination plan was forged after a July meeting of the Advisory Committee on Immunization Practices, an independent group of experts that advises the CDC on vaccine policies.

They agreed to create five broad priority groups totaling 159 million people - pregnant women, healthcare workers, people with asthma or other conditions that put them at high risk of flu complications, caregivers of infants too young to be vaccinated, and children and adults aged up to 24.

Lieberman said he thought HHS and CDC should have revised the priority groups downward to the 42 million people deemed most in need of vaccination, but Schuchat said the committee met again in October and decided not to modify its recommendations.

“What we heard pretty consistently was leave the flexibility to the state and locals. Let them decide,” she said. Many wanted to run school-based clinics and narrowing the designated priority groups would have meant the most available vaccine - the spray - could not be broadly used.

Dr. Nicole Lurie of HHS said the government and Congress need to invest more in public health. “Our nation’s investment in public health infrastructure, particularly at the state and local levels, remains a critical challenge that has real life consequences,” she said.

Separately, vaccine maker Novartis AG said a half-dose of its H1N1 vaccine may be enough to generate a protective immune response. That could in theory stretch the U.S. vaccine supply but would have to be approved by regulators.

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* Senators call U.S. response confusing, misinformed

* Officials say decisions must be made at local level

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)