Speaking on an RTHK programme, Ho said people may not know whether they belong to the priority groups set out by the government.
Ho was speaking a day after the government said booster shots will be available from November 11, and bookings will open on Friday for the elderly, medical staff, patients with weak immune systems, and workers at high risk places.
An estimated 1.86 million people will be eligible.
“All the vaccinated people have provided their phone numbers. The government can contact them and tell them they are advised to get a third jab, and then make the arrangements for them so they will be clearer about it,” Ho said.
“In terms of anti-epidemic control, and when it comes to reopening the border, the key is to vaccinate people who may come in contact with patients. This includes airport, quarantine hotel staff and cross border drivers,” he said.
“The government knows who they are and where they are, and how many of them there are. The government can make arrangements so it’s more convenient for them to be vaccinated,” he added.
Meanwhile, Food and Health Secretary Sophia Chan reassured the public that there won’t be a shortage of Covid-19 vaccines even if the inoculation rate picks up after booster shots become available.
The government had said last week that Hong Kong has about 1.7 million BioNTech jabs left, but Chan said if demand grows, the administration is ready to buy more vaccines.
“We have been monitoring closely. People don’t have to worry about a shortage of any types of vaccines. At present, we are in contact with the drug manufacturers and there should be sufficient supply,” she said.