Patients with severe cases of swine flu are reacting poorly to antiviral drugs such as Tamiflu, and they are more likely to develop inflammatory infections even though the virus in their body is weakening, the latest University of Hong Kong study shows. The university also estimated that more than 300 people could die in the second wave of the pandemic, which is expected to peak next month. The findings were announced yesterday, as the government launched its free vaccination scheme for people in five high-risk groups. A total of 1,528 people were inoculated. HKU scientists compared 37 severely ill swine flu patients with 37 mild cases. All the 13 patients who died had severely damaged lungs, and some had blood clots, inflamed hearts or haemophagocytosis, a condition where white blood cells become so active that they attack healthy cells. White blood cells usually defend the body against infections. 'Even when they had recovered, we are uncertain how much of their lung function had been damaged,' said Professor Yuen Kwok-yung, head of the university's microbiology department, who led the study. He said antiviral drugs such as Tamiflu and Relenza worked best when taken within 48 hours of the onset of symptoms. But the people they studied who had the most severe cases of swine flu sought help only five to seven days later, meaning the drugs were no longer useful. The virus slowly weakened in the body, he said. The study will be published in the journal Clinical Infectious Diseases. One-fifth of the severely ill patients had been otherwise healthy and 23 required respirators. They spent 14 to 30 days in hospital. Yuen said statistics from Australia and Canada indicated that more than 300 people in Hong Kong could die from swine flu during the peak winter infection period, including up to 56 otherwise healthy people. 'If they take the vaccine, they will not die,' he said. Yesterday was the first day the public could get inoculated at 220 public clinics. Those who were vaccinated comprised 928 people aged 65 or above, 296 chronic patients, 196 children aged between six months and six years, 98 medical workers, four pregnant women and six pig farm or slaughterhouse workers. Sixty per cent of the 495 children booked for the jab did not show up. Government clinics can handle 6,000 shots per day. In view of the situation, Centre for Health Protection controller Dr Thomas Tsang Ho-fai said parents no longer had to book appointments for their children. Aside from a media campaign, the centre will organise talks at kindergartens and nurseries. 'To increase the number of children getting vaccinated, our staff members will call each kindergarten and nursery,' Tsang said. Soyi Mo, mother of an 18-month-old boy, said she had her baby vaccinated because she had been infected before. 'I am very worried that my son will catch swine flu too,' she said. A Mrs Chan, who has two-year-old twins, said she was more worried about her daughters developing resistance to Tamiflu rather than developing side effects from the vaccine. 'If the twins catch the flu, the whole family will be infected too,' she said. Senior medical staff at Queen Mary Hospital and HKU were inoculated, including Yuen and Professor Fan Sheung-tat, the university's head of surgery. Yuen was inoculated using a new technique called intradermal injection, where the vaccine is directly injected into the dermis. He said the method would generate a quicker immune response and the amount of vaccine needed was only one-fourth to one-third of the normal load. However, it was 'much more painful' than the normal injection and not many people used it. People can get the shots from private clinics from next Monday. Those vaccinated before then would not be eligible for the government subsidy, undersecretary for food and health Professor Gabriel Leung said. A 57-year-old swine flu patient with a history of hypertension, hyperlipidemia and heart disease died in North District Hospital at 12.35pm yesterday. He developed fever and a cough on December 11 and went to the hospital on December 15. He was prescribed Tamiflu and antibiotics. A 30-year-old woman previously in good health was in critical condition with swine flu in Queen Mary Hospital. She visited the hospital on Saturday and was prescribed Tamiflu and antibiotics. She was transferred to the intensive care unit yesterday.