Compared with the same period last year, China has observed a higher level of flu activity nationwide since March, with a notable increase of flu activity in its southern and northern regions particularly after September, a leading medical expert said on Sunday.

It means there's a risk that COVID-19 outbreaks might combine with the incidences of respiratory infectious diseases during the upcoming winter and spring seasons, said Wang Huaqing, chief expert of immunization program at Chinese Center for Disease Control and Prevention.

He made these remarks at a news conference of the State Council inter-agency task force for COVID-19 response held in Beijing.

"As countries around the world took measures to curb COVID-19 since its outbreak last year, we've seen that the flu activity also fell compared to the past flu season," he said.

"However, entering 2021, the flu activity has increased, with the respiratory infectious disease having spread in some countries."

Wang said the flu vaccine is the most effective way to guard people - especially infants, children and the elderly against the influenza, as it can reduce the risks of flu infection and serious complications. These people are also among the priority groups to get the flu vaccination, he added.

A minimum 14-day interval is required between the flu and COVID-19 vaccines, he said.