Shu Yuelong, director of the Chinese National Influenza Centre, said the first mutated strain of the (A)H1N1 virus was detected in June in a case imported from Britain and a similar strain was detected three months later in the eastern province of Zhejiang.
The mutation detected recently was an isolated case and the cases were not connected.
This kind of mutant virus has been found in patients with slight and heavy symptoms as well as those who have recovered. The virus has not widely spread so far yet.
A mutation had been found in samples of the swine flu virus taken following the first two deaths from the pandemic in Norway and the similar mutation had been observed in Brazil, China, Ukraine, and the United States, as early as April.
