Local researchers have proven antibodies from the plasma of recovered swine flu patients are an effective treatment for those with severe complications from the virus that sparked a global pandemic last year. This emerged yesterday as Mexico lifted its alert for swine flu, officially ending the health emergency in the country where it began 14 months ago. A joint study by the University of Hong Kong (HKU), the Hong Kong Red Cross and the Hospital Authority - details of which have yet to be published - has concluded antibodies from the plasma of recovered patients can kill the H1N1 virus in severely ill patients. Researchers say a similar treatment may also be effective against other viruses, including new ones. About 30 swine flu patients in critical condition underwent the treatment after they did not respond to the antiviral drugs Tamiflu and Relenza and most were cured. Some were treated with the plasma, known as convalescent plasma, while others received a more concentrated hyperimmunoglobulin made from it. HKU clinical assistant professor of medicine Dr Ivan Hung Fan-ngai, who led the study, said antibody therapy could be the 'last defence' against swine flu. 'We used the antibodies on severe swine flu patients who did not respond to antiviral treatment, neither oral nor intravenous,' he said. 'Some of them died subsequently, but we have enough evidence to conclude that the antibodies are an effective cure, as most patients have since recovered.' The H1N1 virus surfaced in Mexico in March last year. The World Health Organisation declared a pandemic in June after 74 countries and territories reported cases. The virus broke out in 214 countries and killed at least 18,209 people. In Hong Kong, 282 patients had severe complications, of whom 80 died. Although the worldwide pandemic and seasonal influenza activity have now abated, scientists and doctors are in a race to find new weapons against the ever-changing flu virus. Antivirals such as Tamiflu are effective only if they are given early enough, preferably within 48 hours of the onset of illness. Rising drug resistance also means an alternative treatment is needed. 'While vaccination remains the most effective prevention of flu, our study shows that an antibody therapy is an effective treatment, which can possibly work on other viruses including newly emerged ones,' Hung said. 'Swine flu may strike again this summer, no one will know for sure.' Hung said HKU had developed a similar antibody therapy for Sars patients in 2003 but there was insufficient data to show its effectiveness. Since August last year, HKU's microbiology department and the Red Cross Blood Transfusion Service have, through a HK$3 million research project, recruited 881 recovered swine flu patients as potential blood donors. About 300 litres of plasma was subsequently collected from 680 people. The research team then sent 276 litres of convalescent plasma to Australia to produce hyperimmunoglobulin - highly concentrated doses of antibodies against the pandemic H1N1 virus - which can treat up to 40 patients. A further 20 litres of plasma, enough to treat another 40 patients, was stored in Hong Kong. Between January and April this year, fewer than 10 patients in Hong Kong were given the hyperimmunoglobulin, and about 20 others received plasma. Antibody therapy is used only on patients who are on a ventilator in intensive care, do not respond to antiviral treatment, and have had flu symptoms for less than seven days. In a separate study published in the online version of international medical journal Clinical Infectious Diseases last week, the research team reported that 90 per cent of the potential blood plasma donors have a high enough level of antibodies - 1:40 in technical terms - to protect themselves from another swine flu infection and to make hyperimmunoglobulin. Of these, a fifth have a high antibody level of 1:160 or above. Hung, also a specialist in infectious diseases, and HKU's head of microbiology, Professor Yuen Kwok-yung, were the study's two main researchers. 'As some donors have a very high level of antibodies, we used their plasma directly on some patients before the hyperimmunoglobulin was made available,' Hung said. 'The making of the hyperimmunoglobulin took about two months so the plasma was used as an emergency treatment.' Hung said the project would recruit more donors if there was a second swine flu outbreak. 'We thank the donors very much. They have spent several hours donating plasma ... extracting plasma is a much longer process than just taking blood.'