A swine flu virus outbreak that has rapidly claimed up to 68 lives in Mexico, and infected people in the US, was last night declared a "public health emergency of international concern". The decision, made by the World Health Organisation (WHO), means that countries are now being asked to step up surveillance for any cases. Travel advisories, trade restrictions, and even border closures could follow.
WHO's director-general Margaret Chan said the disease involves "an animal strain of the H1N1 virus, and it has pandemic potential". And the verdict of the US Centers for Disease Control and Prevention was that the new flu has already spread so widely that it cannot be contained. As if to emphasise this, within a few minutes of the WHO's declaration, cases of swine flu were confirmed in both New York and Kansas, to add to those already in California and Texas.
And, last night, it was reported that a British Airways cabin crew member was taken to hospital after falling ill with flu-like symptoms on a flight from Mexico City. A Health Protection Agency (HPA) spokesman said in a statement: "At present, there have been no confirmed cases of human swine flu in the UK or anywhere in Europe." And there is hope that the illness is responding to known, and widely stocked, medicines.
The seat of the outbreak is – for now at least – in Mexico, where more than 1,000 people have already contracted the virus. Last night, the government there empowered health departments to isolate patients and inspect homes, and President Felipe Calderon appealed for calm. All public events have been cancelled for 10 days, and serious precautions are being taken in many other countries. In Japan, devices have even been installed at Tokyo's largest airport to take the temperatures of passengers.
The particular virus in question is known as A/H1N1, a flu variant that has not previously been seen in pigs or humans, though other types of H1N1 have. Initial evidence indicates it has spread between people. Seasonal flu vaccine is not believed to protect against the new flu, but antiviral drugs Tamiflu and Relenza appear effective against the H1N1 virus.
The US has large stocks of Tamiflu (as does the UK, thanks to fears of bird flu), but Mexico has enough to treat only a million people – a mere one in 20 citizens of greater Mexico City. Officials said the medicine will be strictly controlled and handed out only by doctors. A "seed stock" genetically matched to the new swine flu virus has been created by the Center for Disease Control and Prevention. If vaccine production is necessary, manufacturers would need that stock to get started. Producing the vaccines could take months.
But it may be too late to contain the outbreak, given how widespread the known cases are. If the confirmed deaths are the first signs of a pandemic, then cases are probably incubating around the world by now, said Dr Michael Osterholm, a pandemic flu expert at the University of Minnesota. This outbreak is particularly worrisome because deaths have happened in at least four different regions of Mexico, and because the victims have not been vulnerable infants and the elderly. The most notorious global flu pandemic, thought to have killed at least 40 million people in 1918-19, also first struck healthy young adults.
Scientists have long been concerned that a new killer flu could evolve when different viruses infect a pig, a person or a bird, mingling their genetic material. The resulting hybrid could spread quickly because people would have no natural defences against it. No vaccine specifically protects against swine flu, and it is unclear how much protection human flu vaccines offer.
In Mexico, authorities have closed schools, museums, libraries and theatres in an effort to contain the outbreak. Sold-out games between Mexico's most popular football teams are being played in empty stadiums. Health workers are ordering sickly passengers off public transport. And while bars and nightclubs filled up as usual, some teenagers were dancing with surgical masks on.
Across their overcrowded capital of 20 million, Mexicans are reacting with fatalism and confusion, anger, and some fear at the idea that their city may be ground zero for a global epidemic caused by a strange mix of human, pig and bird viruses. Officials urged people to stay home if they felt sick, and to even avoid shaking hands or kissing people on the cheek. Health workers also staffed the international airport and bus and metro stations, handing out masks and trying to steer away anyone who appeared sick.
Mr Calderon said his government discovered the nature of the virus late on Thursday with the help of international laboratories. "We are doing everything necessary," he said in a brief statement. This seems not to be the whole story, and Mexico appears to have lost valuable days or weeks in detecting the new virus.
Health authorities started noticing a threefold spike in flu cases in late March and early April, but thought it was a late rebound in the December-February flu season. Testing at domestic labs did not alert doctors to the new strain, although US authorities detected an outbreak in California and Texas last week.
Perhaps spurred by the US discoveries, Mexico sent 14 mucous samples to the CDC on 18 April and dispatched teams to hospitals looking for patients with severe flu or pneumonia-like symptoms. These teams noticed something strange: the flu was killing people aged 20 to 40. Flu victims are usually either infants or the elderly.
Then, mid-afternoon Thursday, the Mexico City health secretary, Dr Armando Ahued said officials got a call "from the United States and Canada, the most important laboratories in the field, telling us this was a new virus". WHO has now sent experts to Mexico to monitor the situation.
The cases in New York and Kansas are, at present, ambiguous. Tests confirmed that eight city schoolchildren had a type-A influenza virus, likely to be swine flu, the New York city health commissioner, Dr Thomas Frieden, said on Saturday. Samples have been sent to the US Centers for Disease Control and Prevention for further testing to see if they are indeed the unusual H1N1 flu strain.
But if the children have contracted the same virus, then the progress of their illness offers some hope. "In every single case, illness was mild. Many of the children are feeling better," Dr Frieden said. And some reports from Mexico last night offered further hope. Doctors said that antiviral medications and even steroids were working well against the disease, and noted that no new deaths had been reported in the capital in 24 hours.
Asia, the centre of the H5N1 bird flu virus which has killed at least 257 people worldwide since late 2003, is being especially cautious. Japan's biggest international airport has stepped up health surveillance, with officials installing a device at the arrival gate for flights from Mexico to measure the temperatures of passengers, while the Philippines said it may quarantine passengers with fevers who have been to Mexico. Health authorities in Thailand and Hong Kong said they were closely monitoring the situation.
The virus appears to cause flu-like symptoms that can develop into severe pneumonia, a WHO spokesman said, urging anyone to visit a doctor if they had been to affected areas and were experiencing any symptoms. "You would want to take the same precautions that you would do with pneumonia and an influenza-like illness," he said.
The WHO seems to have reacted swiftly. Dr Chan abandoned appointments in Washington to fly to Geneva, and an emergency committee of 15 experts from all regions, including specialists in epidemiology, laboratory testing, clinical treatment of cases, and travel, met there yesterday for some hours.
It "agreed that more information is needed" before a decision could be made concerning any change in the pandemic alert level, currently three on a scale of one (low risk of human cases) to six (efficient and sustained transmission between humans). Keiji Fukuda, acting WHO assistant director-general for health, security and the environment, said: "It is too early to say whether things are changing for better or worse."