Hong Kong has secured Covid-19 vaccine bookings for 35 per cent of its population, with frontline health workers and other at-risk groups likely to be among the first to receive the shots, as the city expects to record 21 cases on Sunday.The worrying daily infection figure from sources came after just seven cases were confirmed on Saturday, the lowest in two months.Government adviser Professor David Hui Shu-cheong said the Department of Health had placed a deposit for vaccines developed by…