I do not believe anything is *required* for HK. penguinsix has given you the link that is recommended and followed by majority of parents&kids but they are just that, recommendations.
A few parents (generally short term temp expats) ignore those recommendations and decide to go with whatever their home country follows.
A few parents ignore science and doctors and choose instead to believe a nude model, z-list actress and other similar quacks and choose not to immunize at all.
Every school that I've ever come in contact with has asked for a copy of immunization record to check children have some minimal set.