A genetically mutated H1N1 swine flu virus resistant to the Rapiacta flu drug has been detected in a 5-year-old patient, according to the National Institute of Infectious Diseases.
It is likely the first case in Japan concerning a patient treated with the intravenous drip medicine, which was introduced in January 2010.
According to a recent report by the institute, a genetic mutation was found in a virus from the child, who was treated with Rapiacta after testing positive last month for the type A influenza virus.
"This is only one case and there is no need to worry," said Takato Odagiri, head of the Influenza Virus Research Center at the institute.
The institute said the virus from the child was also resistant to Tamiflu, another flu drug, but was not resistant to Relenza and Inavir.
The boy has already been discharged from the hospital.