Thousands of people in the UK have now caught swine flu
Further deaths from swine flu without there being underlying health problems cannot be ruled out but will be rare, England's chief medical officer says.
It follows the first death in the UK of a patient who was otherwise healthy. The victim lived in Essex and died in hospital on Friday.
Sir Liam Donaldson said it was a tragic case but people should not panic.
Fifteen people have now died in the UK after contracting swine flu - 13 in England and two in Scotland.
Sir Liam said that for the vast majority of people infected, the new flu virus had produced only mild symptoms.
"When it has produced severe illness it's tended to be people with underlying health problems, in this case it was in a previously healthy adult and we've seen from other cases around the world that uncommonly this does occur," he said.
"But it shows that all our planning, all our efforts, the stockpiling of anti-virals, the fact we will be one of the first countries to get a vaccine, all of those measures are extremely important."
The family of the Essex victim have asked for no more details of their relative to be released.
BBC health correspondent Branwen Jeffreys said the death had come as no surprise to most experts and was a reminder of the potential threat posed by all kinds of flu.
"It can lead to complications such as bronchitis and pneumonia," she said.
Professor Steve Field, chairman of the Royal College of GPs, said the death was not a significant development in terms of the pandemic's progress.
"We see some deaths each winter in healthy people, or apparently healthy people, through the seasonal flu," he said.
"And we know there have been a number of deaths in America, who've had a much larger outbreak so far than we have.
"I mean this is very sad for the individual's family but the system we've got here in the UK is very good."