GENEVA : The World Health Organization on Tuesday urged travellers to wear masks on planes and keep themselves informed as COVID-19 cases surge again in some countries, prompting new restrictions in places like Australia.Spokeswoman Margaret Harris urged people not to be caught off-guard by resurgent local epidemics and quarantine measures, saying: "If it's anywhere, it's everywhere and people travelling have to understand that.""This virus is widespread and people have to take that very, very seriously."The WHO said last month that it would update its travel guidelines ahead of the northern hemisphere summer holidays but they have not yet been released.In the meantime, travellers should "remember things will change, or may well change",.