The World Health Organisation said a lack of data was making it challenging to help China manage the risks of a COVID-19 surge over the Lunar New Year holiday, as the world's second-largest economy reopens after three years of isolation. The holiday, known before the pandemic as the world's largest annual migration of people, comes amid an escalating diplomatic spat over COVID curbs that saw Beijing introduce transit curbs for South Korean and Japanese nationals on Wednesday. The virus is spreading unchecked in China after Beijing abruptly began dismantling its previously tight curbs in early December following historic protests. The…