BEIJING, Jan. 9 (Xinhua) -- The predominant virus strains this winter have been little seen in recent years, which has caused the current influenza outbreak in China, according to an official at the National Health and Family Planning Commission.

People have been more likely to lack the immune barrier for the strains, adding to the susceptible population, said Jiao Yahui, deputy head of the medical administration and management bureau of the commission, at a press briefing Tuesday.

However, no mutation has been detected in the strains which could affect virus transmission, disease severity or drug resistance, Jiao said, noting that current neuraminidase inhibitors, which are used to shorten duration of flu, are still effective.

According to the Chinese National Influenza Center, flu has been on the rise in recent weeks, and was very prevalent during the last week of 2017 with 11,253 cases reported, up from 7,730 the previous week.

As for hospitals where relevant drugs were unavailable, the commission has asked local health and family planning departments to open up temporary channels for local medical institutions to procure drugs in order to ensure adequate supply of the medicine, according to Jiao.