Beijing Five Hong Kong medical chiefs went to Beijing to find out more about the mainland's new swine flu serum. The heads of medical departments and centres were there to tour Sinovac's factory. The mainland approved Sinovac's vaccine two weeks ago and the Hong Kong experts are checking how safe it is. Background Countries have been racing to find a vaccine for swine flu. Doctors and scientists will look at long-term side-effects. Hong Kong is looking to buy HK$700 million worth of vaccines. The government will soon decide who to buy from. The one-shot Sinovac vaccine is being used in a nation-wide programme launched last week. Some 100,000 students will get the shot. Sinovac trials showed 85 per cent of users developed antibodies against swine flu after three weeks.