But it could have been much worse. The new strain of H1N1 flu could have been much more virulent, and it could have been bird flu, which, due to the way the United States produces flu vaccine, could wreak havoc.

Months back, when a swine flu vaccine was still just a glimmer in scientists’ eyes, US health officials were driving home the message that children, and especially those with underlying health conditions like asthma, and pregnant women were at greater risk of dying from H1N1 influenza and should be first in line for inoculation.

But after rolling out the vaccine early last month, the authorities ran into a problem: there was not enough to go around.

"The National Institutes of Health and Centers for Disease Control and Prevention have done a very good job of emphasising the importance of getting vaccinated. But then there’s no vaccine," said Steven Salzberg, director of the Center for Bioinformatics and Computational Biology at the University of Maryland.

Salzberg’s wife and younger daughters were among thousands who queued last week in Rockville, a suburb of Washington, for swine flu vaccinations.

"They left when they saw the line was about half a mile long (1 km) before the place was even open. There were many, many hundreds of people and more were arriving by the second," Salzberg told AFP.

Last week, as child deaths spiked well above the annual toll for children from seasonal flu, vaccination clinics in the county that includes Rockville were abruptly cancelled.

The county’s supply of vaccine had run dry. On Friday, Montgomery had 250 injectable vaccine doses left, and only 8,800 people out of a population of one million who live in Montgomery County had been innoculated.

So what if this had been the next "big one", a flu on the scale of the pandemic that killed tens of millions around the globe in 1918? After all, the strain of flu that caused the 1918 pandemic was also H1N1, the grandfather of today’s swine flu pandemic.

"If we had a really virulent highly infectious influenza strain today, it could easily be as bad as 1918," said Salzberg.

"It could be worse because we mix so much more. We travel faster," he said.

But David Beshai, associate professor at the Johns Hopkins Bloomberg School of Public Health, said progress in health care and nutrition meant a replica of 1918 was not on the cards.

"The 1918 pandemic that killed so many people happened in a different world. Nutrition was so poor, our hospitals were so useless, you couldn’t get on a ventilator in an intensive care unit," Beshai said.