Hong Kong’s third wave of Covid-19 infections led to nearly 4,000 people contracting the virus between early July and late last month, 98 of whom died, but the fight is far from over. In the second of a three-part series, the Post identifies high-risk groups as a fourth wave looms, and looks at what the city has learned – and hasn’t – from its past experience in combating the pandemic.Schools, domestic helpers and subdivided flat tenants are sitting ducks for a possible fourth wave of Covid-19…