The great urban migration that has helped propel China's meteoric rise has also raised some social issues. The need for reform of the household registration system, which restricts migrants' access to health, education and welfare, is well documented. But some problems arise from the challenge of keeping track of a huge mobile population. One of them is the spread of measles, a disease Beijing planned to virtually eliminate by 2012 with a vaccination campaign.
At the end of last year China had about 245 million migrant workers, accounting for 18 per cent of the population. The disease is making a comeback among them because millions of their children are slipping through the vaccination net. Low awareness of the need for vaccinations compounds the difficulty of tracking them.
The gap in community protection is reflected in comparative inoculation figures for migrant and non-migrant families. According to a survey by Beijing health authorities, more than 92 per cent of permanent residents' children have had measles shots, but the rate drops to 54.7 per cent in some areas with a high proportion of migrant workers. The adverse health implications are illustrated by the inoculation threshold known as community herd immunity - the proportion of immune people above which a contagious disease may no longer persist. For measles, an airborne disease, it is a relatively high 83 to 94 per cent.
In the first five months of the year, the mainland recorded 35,677 cases of measles, a viral disease characterised by a skin rash and fever, compared with 27,646 for the whole of last year. The resurgence has undone the good of the vaccination of nearly 100 million children in 2010 in response to a call by the World Health Organisation to combat measles. Community education about the need for vaccination has an obvious part to play. But reform of the household registration system would be an effective way of bringing preventive health care to migrant workers and their families.