The World Health Organization (WHO) recommends constant monitoring for H7N9 bird flu outbreaks in China but cautioned that the risk of sustained human-to-human transmission is low.

Outbreaks of H5 bird flu strains in poultry and wild birds across Europe, Africa and Asia are also raising concern, the WHO said, and while the human risk of these outbreaks is also low for now, vigilance is vital.

“Constant change is the nature of all influenza viruses – this makes influenza a persistent and significant threat to public health,” Wenqing Zhang, head of the WHO’s global influenza program, told reporters on a telephone briefing.