According to the article the law has been in effect since 1994 and is only now being enforced. The government claims that the number of people who died from being bitten by a rabid dog was 13, more than double the year before.
With more that 1 million dogs in Beijing, most are not vaccinated for rabies. So, rather than enforce or create the vaccination laws, they are banning the dogs.
Here's the full article. Beijing Bans Big & Vicious Dogs
|Big & Vicious Dogs Banned|