Another 11 cases of swine flu have been confirmed in England, bringing the UK total to 229. The new patients include a boy from Camden, north London, and a woman from Tower Hamlets, in the east of the capital, who had both returned from countries affected by swine flu. Three children in the Midlands also have the illness, and the cause is under investigation by the Health Protection Agency (HPA). An adult in the North West, linked to another patient already confirmed as having the disease, has now developed swine flu. Another two cases - one in Yorkshire and Humber and another in Scotland - are also travel-related. A number of schools, including top public school Eton, have been forced to close because of the disease in recent weeks. UK scientists have now produced a strain of the swine flu virus that is more suitable for making a vaccine. The move is a "crucial step" towards the large-scale production of a vaccine against the disease, the HPA said. The virus strain was developed at the HPA's National Institute for Biological Standards and Control (NIBSC), based near Potters Bar in Hertfordshire. It is now being made available to drug manufacturers and other flu laboratories worldwide.