The Bird Flu or H5N1 strain is potentially making a resurgence.

The deadly flu is resistant to most recent vaccines and cases in China and Vietnam are causing concern.

The UN’s Food and Agriculture Organization (FAO) on Monday urged increased surveillance and preparation for a potential outbreak of the virus, which it says has infected 565 people since it first appeared in 2003, killing 331 of them.

The virus was eliminated from most of the 63 countries infected at its peak in 2006 after mass poultry culling, but since 2008 it has been expanding geographically in both poultry and wild birds, partly due to migration patterns.