US officials have warned of delays in the delivery of swine flu vaccines² just as deaths from the H1N1 virus climb above epidemic³ level in some states.

美国官方对猪流感疫苗的推迟发售进行预警，某些州H1N1病毒致死率攀升至传染病水平。

Some 11.4 million vaccines have been made available in the US

Only 28-30 million doses would be available by the end of the month, said Anne Schuchat of the US Centers for Disease Control and Prevention (CDC).

That was down from an earlier estimate of 40 million.

Swine flu has had an especially strong impact on children, 86 of whom have died this year, Ms Schuchat said.

The number of children who have died so far this year from the H1N1 virus was greater than the number that normally die in an entire flu season, Ms Schuchat said.

Forty-three children are reported to have died from flu since 30 August, with 38 of those confirmed to have been caused by the H1N1 virus.

Half of those deaths were in children aged⁴ between 12 and 17.

"These are very sobering（使清醒的，使冷静的） statistics," Ms Schuchat said. "Some of these children have been totally healthy."

'Rapid deterioration⁵'

Ms Schuchat said swine flu activity was widespread in 41 states, and deaths had reached the epidemic threshold（极限，门槛） in some states and cities.

"Influenza⁶ is widespread in the country and illnesses, hospitalisations and deaths continue to increase," she said.

"It's unprecedented⁷（空前的） for this time of year to have the whole country seeing such high levels of activity."

Testing the vaccines for strength and purity was cited as one reason for a delay in their delivery.

"We are not cutting any corners in the safety of the production of this vaccine¹ or the testing and oversight⁸ of the vaccine," Ms Schuchat said.

Some 11.4 million vaccines have so far been made available in the US.

At a meeting on swine flu in Washington, officials from the World Health Organisation⁹ said the H1N1 strain was killing¹⁰ unusually quickly.

"In severe cases, patients generally begin to deteriorate¹¹（恶化） around three to five days after symptom（症状，征兆） onset（攻击，进攻）," said the WHO's Nikki Shindo.

"Deterioration is rapid, with many patients progressing to respiratory failure（呼吸衰弱） within 24 hours, requiring immediate¹² admission to an intensive care unit."