With the World Health Organization discussing whether to declare, as Nature went to press, that a swine influenza pandemic has arrived, doctors, scientists and government officials say the enormous preparedness efforts of recent years have aided the world's response to the virus.

Britain has sufficient stockpiles of antiviral drugs to protect 50% of its population. Credit: K. COLLINS/REUTERS

"Clearly, the global preparedness for dealing with an influenza outbreak is much better now than it was five or six years ago," says virologist Malik Peiris of the University of Hong Kong.

But there have been some hiccups, due largely to the mismatch between the pandemic scenarios envisaged and the one that has arrived. Most nations had prepared for a pandemic sparked by the deadly A(H5N1) avian influenza virus, which kills up to 60% of those infected, but the A(H1N1) swine flu virus epidemic has been much less severe so far.

"Many nations built their plans around the idea that a pandemic strain would evolve in southeast Asia, that we would recognize it early, and that we would be able to contain it," says Eric Toner, a physician and preparedness analyst with the University of Pittsburgh Medical Center's Center for Biosecurity in Pennsylvania. "None of that turned out to be true."

The idea that one could trap it at the early stages was certainly not successful.

Global pandemic planning efforts were ramped up after severe acute respiratory syndrome (SARS) swept through Asia in 2003, and the deadly H5N1 strain emerged in the same year. Local, national and international entities involved in flu response are now better coordinated, observers say.

That was evident with regard to the current situation, as officials — for instance, at the US Centers for Disease Control and Prevention in Atlanta, Georgia — delivered open and consistent public messages about the seriousness and uncertainty of swine flu infections, says Georges Benjamin, executive director of the American Public Health Association in Washington DC. That's in contrast to 2001, when some conflicting messages were delivered during the anthrax attacks.

In some countries, pandemic planning has led to stockpiled antiviral medication (see 'Preparedness by the numbers') being distributed to treat people with swine flu and their contacts. And the boost in research spending on epidemiological modelling and laboratory studies has enabled scientists to understand the H1N1 virus in record time, prepare to manufacture more vaccine faster, make more informed decisions on how to intervene in the virus's spread, and understand and share information on its genetic characteristics.

"We got an extraordinary laboratory understanding of this virus in a very short period of time, and that is the scientific 'wow' of what really happened in this outbreak," says Benjamin.

But the divergence between the anticipated pandemic and the one that has actually arrived has caused some glitches. For instance, the swine flu virus was not detected in time to contain it, as had been envisaged in some scenarios involving avian flu. "By the time the surveillance systems picked [the virus] up, it was already spreading way out of control, so the idea that one could trap it at the early stages was certainly not successful," says Peiris.

As swine flu began to spread throughout North America, which had hoped to have weeks of warning before a virus arrived from Asia, officials were initially confused about how to implement response plans. For instance, swine flu symptoms were milder and less severe than anticipated — impossible to distinguish from seasonal flu — and hospitals and health departments were swamped with people seeking tests for swine flu. A report issued on 4 June by the non-profit group Trust for America's Health, based in Washington DC, also noted that budget cuts at health departments at all levels slowed the US response, for instance by delaying testing.

"We have to consider what happened in the month of May as maybe a warning of what's coming, and we're working very hard this summer to have countermeasures available if the need for those arises" in the autumn, says Robin Robinson, principal deputy director of the Biomedical Advanced Research and Development Authority within the US Health and Human Services department.

By contrast, Asia had expected an avian pandemic virus to arise in its backyard and was not fully prepared for swine flu from overseas. Most of the flu plans for the members of the Association of Southeast Asian Nations "focus on how to cull chickens", says Hitoshi Oshitani, a virologist with the Tohoku University Graduate School of Medicine in Sendai, Japan. "They may have some rapid containment plan, but containment is not possible for this current virus," he says.

Some Asian countries have applied containment measures that had little chance of working. China, for example, quarantined foreign travellers with fever symptoms and symptomless travellers in contact with those, a move not backed by scientific evidence, Toner says.

When the virus spread to Europe, some nations found they were not as ready as their thorough plans had led them to believe they were. For instance, Britain's Health Protection Agency, which was responsible for investigating the initial swine flu cases, did not at first have enough staff available to carry out the investigations, says Sandra Mounier-Jack, a health-policy analyst at the London School of Hygiene and Tropical Medicine. And a planned telephone line that was to have been used to help distribute antivirals had not been set up when swine flu appeared.

These are common problems, says Mounier-Jack. "The major gaps are about making the plans operational — making sure that people at local levels know their roles and responsibilities, even in countries which have very good plans and are rich."

And some long-standing challenges for Europe have still not been addressed, such as the piecemeal nature of the response. "We have 27 pandemic preparedness plans in different states of maturity, and now individual ministries of health are all lining up to buy up vaccines," says Albert Osterhaus of the University of Rotterdam in the Netherlands.

But perhaps the biggest global challenge is arriving now, as the Southern Hemisphere enters its flu season and swine flu threatens many of the least-ready countries. "In general, the developing countries are not prepared," Oshitani says. The World Bank has released billions of dollars for preparedness in these regions, but many developing nations still do not have plans for dealing with a pandemic — and some that do have simply cut and pasted versions of plans from developed countries, which do not apply to poorer nations unable to afford vaccines and antivirals.

People in poor nations already suffer from a higher incidence of conditions, such as malnutrition and HIV, that make them more vulnerable to the new virus. In addition, they are likely to be left out of the global scramble for a vaccine, which has already started as nations such as the United States and Britain rush to tie up vaccine contracts.

On the whole, Oshitani says, "this pandemic came too early. If we had had two more years, we would have been better prepared."

For Nature 's ongoing coverage of the H1N1 outbreak, see www.nature.com/swineflu.