Swine flu has caused global concern for nine days and been detected in 18 countries, but vital questions about the virus remain. The World Health Organisation has upped its alert to one level off declaring a pandemic and suggested that that moment may come soon. Governments have responded with measures from quarantining suspected sufferers, to travel restrictions and trade bans. In a number of instances, science has been ignored in favour of common sense and politics. Hong Kong has handled the situation sensibly. The Mexican man who was found on Friday to have been infected has been isolated. Guests and staff at the hotel in Wan Chai where he was staying have been quarantined for a week. Efforts to find others at the hotel and on the flight that brought him here from Shanghai are continuing. Such steps may seem draconian to outsiders, but they are far from that given our experience in 2003 with Sars. The circumstances are hauntingly similar to how that outbreak began: a doctor with the then little known disease infected fellow guests at their Kowloon hotel. We did not know about the virulence of the virus and how easily it was transmitted until too late; the knowledge we gained taught us not to take chances. Just as was the case with Sars when it initially began spreading here, there are significant questions about the swine flu virus. Available evidence so far suggests that Mexico appears to be the epicentre, though there are also reports indicating the virus might have originated in California. Anyhow, Mexican health authorities have dramatically decreased the death toll attributed to it since it appeared last month. The only death outside the country is a child taken from there to the US for treatment. Although the flu has spread around the world, most cases now seem to be mild - but whether this is fully down to the drugs being given for treatment is unclear. How virulent it is and how it is spread and mutating is unknown. In the absence of answers, Hong Kong's approach is prudent. But this cannot also be said of the responses by some other governments. On the mainland, Mexicans are being rounded up and quarantined regardless of whether they are likely to be carrying the virus or have come into contact with someone who has it. Flights to and from Mexico have been suspended. Mexican officials are rightly outraged and advised their citizens to stay away from China. But authorities elsewhere in Asia have taken a similarly dim view of Mexicans. Singapore now requires them to get visas before travelling to the island state, and Vietnam intends to isolate all people who arrive from the nation and other affected areas. Swine flu is inaptly named. It is a combination of bird, swine and human viruses, but there has been no known transmission of it from pigs to people. Despite this, a number of nations have banned the importing of live pigs. Muslim countries would seem to be using the occasion to make political statements, with Egypt and Iraq ordering the slaughter of pigs. Islam prohibits consumption of pork, and Christian populations in both countries are outraged. Scientists are doing their utmost to fill our knowledge gaps about swine flu. In a world of globalised business, trade and travel, we should be vigilant and sensible. We must not panic or overreact. At no time should politics get in the way of what science is telling us.