By Joyce Zhou HONG KONG (Reuters) – Scores of mainland Chinese travellers are rushing to Hong Kong to receive mRNA COVID-19 vaccines, which are not available on the Chinese mainland, as the country grapples with a torrent of infections which have overwhelmed its health system. A private hospital in the special Chinese administrative region of Hong Kong welcomed the first batch of mainland customers on Thursday, just five days after China reopened its borders for the first time in three years, allowing quarantine free travel. Yoyo Liang, a 36-year old Beijing resident, was one of the first cust…