The World Health Organisation has declared a swine flu pandemic.
WHO director general Margaret Chan said the H1N1 virus could no longer be contained and further spread was inevitable. The scientific criteria for a pandemic had now been met, she added.
She said the pandemic was of “moderate” severity: “The overwhelming majority of patients experience mild symptoms and make a rapid recovery, often in the absence of any medical treatment.”
She added: “No previous pandemic has been detected so early or watched so closely in real time at the beginning.”
Earlier, health secretary Andy Burnham had told managers at the NHS Confederation conference it was “vital” that the NHS maintains its national strength in the face of a pandemic.
He said: “It’s not a cause for alarm because it doesn’t change the plans we’ve put in place.
“We have planned very well in this country - it’s a source of pride to people.”
Mr Burnham said the NHS’s flu plan was an “extensive, detailed, broad based consensus”.
“It’s about to be tested so we’ll have to make sure people stick to the script. As conditions change, we’ll have to make sure policies and procedures we’ve put in place are followed,” he added.
Royal College of GPs honorary secretary Maureen Baker said planning for emergencies such as a flu pandemic has been a priority for GPs and surgeries.