The World Health Organisation (WHO) today increased its global tally of confirmed swine flu cases to more than 2,300, as British scientists announced they had worked out the full genetic code for the virus.

Five new cases were diagnosed in the UK today – four schoolchildren and an adult linked to Alleyn's School in Dulwich, south London, which has been closed all week after six pupils were diagnosed with the illness. There are now 39 confirmed cases in the UK.

Mexico remains the worst affected country, with more than 1,100 laboratory-confirmed human cases of H1N1 virus influenza, including 42 deaths. The United States has reported nearly 900 laboratory-confirmed human cases, including two deaths. Another 22 countries have confirmed cases but no deaths.

The latest figures came as the health secretary, Alan Johnson, said the Health Protection Agency, which monitors infectious diseases, had fully mapped the genetic code of the virus.

He said this would help scientists to understand how the virus operates and to identify the parts that can be used to manufacture a vaccine.

On a visit to a laboratory in Hertfordshire, he was told that researchers hope European manufacturers will be able to take delivery of prototypes in the coming months to enable mass production of a vaccine to begin.

Johnson said: "A significant step towards protecting the world's health against swine flu has been taken. We now look to the vaccine industry to produce the required quantities of vaccine as quickly as possible."

The entire genetic fingerprint and sequence of the swine flu virus will now be analysed to learn how the virus behaves as it infects individuals.

At a meeting of Asian health ministers in Bangkok today, the WHO director general, Dr Margaret Chan, said the world was "better prepared for an influenza pandemic than at any time in history", largely because of precautions taken over the threat of bird flu.

She said: "Years of alert and expectation mean that most countries now have preparedness plans. Vaccine manufacturing capacity has increased sharply. Large stocks of antiviral drugs have been produced and procured.

"Right now, treatment courses from the WHO stockpile are being shipped to more than 70 countries in the developing world."

Mexico's ambassador to the United Nations in Geneva said he would raise concerns at the WHO annual meeting later this month about "discriminatory" measures imposed against the country, its people, and its exports because of the flu. China has placed dozens of Mexicans in forced quarantine as a protective measure against the spread of the virus.

Around the world, public opinion seems to be shifting from fear of a pandemic to scepticism as to whether the virus poses a significant threat.

Half of 2,000 Britons surveyed yesterday said they believe the government over-hyped the threat of swine flu, and are now less worried about it spreading.

The research by online polling centre Toluna found two-thirds of respondents thought the government had coped well with the outbreak, while more than half (54%) thought the NHS was well prepared to cope with a possible pandemic.

The report noted a decline in public worry about the virus spreading, with 40% worried about the virus, compared with 50% last week.

Public health officials around the world acknowledge their worst fears about the new virus have yet to materialise. But many experts worry that people will become too complacent and fail to heed warnings if the virus returns in a more dangerous form in the autumn.

"People are taking a sigh of relief too soon," said Dr Richard Besser, acting director of the US Centres for Disease Control and Prevention.

"The measures we've been talking about – the importance of hand-washing, the importance of covering coughs, the real responsibility for staying home when you're sick and keeping your children home when you're sick – I'm afraid that people are going to say, 'Ah, we've dodged a bullet. We don't need to do that,'" he said.