The jury is still out on whether the swine flu epidemic is really dangerous. According to the New York Times, the outbreak may be considerably smaller than authorities had first feared. Of about 900 suspected cases, about 400 people had the swine flu virus. Of these, just 17 have died: 16 in Mexico and one in the US. The disease also seems less virulent outside of Mexico, where it was first detected.

Nonetheless, thanks to air travel, it has spread with incredible rapidity and cases have been reported in about 20 countries -- a sobering reminder of how vulnerable the world is to a plague. Public health experts constantly remind us of the 1918-1919 flu epidemic. That killed 40 million people, including 550,000 in the US.

Just as earthquake aficionados speak of the "Big One" – the earthquake which will tip southern California into the Pacific, public health experts fear that a "Big One" will sweep across the planet. The author of the Gaia hypothesis – that earth is a self-regulating system – James Lovelock, says that sooner or later humanity will undergo a 90% cull. "The number of people remaining at the end of the century will probably be a billion or less," he told New Scientist earlier this year.

Epidemics present public health authorities with a number of tough ethical dilemmas. Here are some which have emerged in discussions in the media over the past few days:

Triage: will there be enough ventilators to help seriously ill patients breathe? If hospitals are inundated they may not have enough of these machines, or of qualified doctors and nurses to run them. In that case, it may be necessary to remove patients who won’t survive to save patients who probably will. And if two patients have an equal chance of survival, who should get the machine? The younger one? The one without a pre-existing medical condition?

Guidelines worked out last year in New York State recommend that decisions like these should be made by "triage officers" rather than doctors caring for the patients. Otherwise the stress could be corrosive. They also recommended excluding people who have had several heart attacks, who have metastatic cancer with a poor prognosis, who have end-stage organ failure or neurological conditions with high expected mortality.

Governments are capable of using public health as a smokescreen for repression. The Egyptian government, for instance, has ordered the destruction of the 300,000 pigs in the country. It did this even though no cases of swine flu have been reported, even though there is no proof that the disease is transmitted by pigs, and even though veterinary experts say that it makes no sense. But pig owners in the largely Muslim country are overwhelmingly Coptic Christians. According to the New York Times, they see this as just another expression of prejudice against Christians.

The weightiest decision will be whether to forcibly isolate and quarantine suspected cases. When SARS struck Canada in 2003, most people with SARS-like symptoms took a public-spirited approach and voluntarily isolated themselves. But not all. During the 1918 epidemic, Americans tended to stay home rather than risk infecting others. But will a less conformist generation continue to be as cooperative?

At the moment, according to guidelines from the US Centers for Disease Control and Prevention, mandatory quarantine measures kick in only when the case fatality rate rises above 1%. But this means that a million people would have to die before public health authorities are given police powers.

Should healthcare workers be forced to care for patients? During the SARS epidemic in 2003, a number of healthcare workers were infected. The Italian doctor who identified the virus died. Do they have a right to withhold their services to protect their own lives and their own families?

How harshly should other measures be enforced? Should people be arrested or fined for not wearing masks, for not closing schools, or for not accepting social distancing measures? Governments will have to balance competing values – autonomy, civil liberties, transparency, due process and capacity to harm. There is a great danger of harsh and heavy-handed application of preventative measures by over-zealous bureaucracies. Remember Operation Clean Sweep in Outbreak, the 1994 Hollywood thriller about an Ebola-like virus? Gung-ho military types nearly obliterate an infected town to save America.

How much money should be spent on creating a flu vaccine? With limited manufacturing capacity, can the money be better spent on combatting the normal winter flu – which also kills people -– or in designing a new vaccine which might not work?

And – not the most pressing issue, to be sure -- what is the name of the disease? The Deputy Health Minister of Israel has announced that swine influenza A (H1N1) will be called "Mexico Flu" rather than swine flu as pigs are not kosher. Names are always a tough call...

Epidemics bring out the worst – and the best – in people. Just read Defoe’s A Journal of the Plague Year, his gripping account of 1665 London battling the bubonic plague. Our time to confront "the Big One" might not have arrived, but we need to prepare ethics as well as vaccines.