Wallace Lau, the convenor of an advisory panel on Covid-19 jabs, told a radio programme that experts would be meeting next week to discuss whether people needed a third Covid jab when their antibodies levels eventually fell.
But the University of Hong Kong professor said it was more important to have a higher vaccination rate first.
Experts have said herd immunity will probably only be achieved when around 70 percent of people have been inoculated. Government figures show just over 40 percent of the population, or 2.73 million people, have so far received one Covid jab.
Professor Lau was also asked about a recent University of Hong Kong study that showed antibody levels in people, who had received two BioNTech doses, were about nine times higher than in those who had had two Sinovac jabs.
He said the effectiveness of a vaccine depended on more than the antibodies it produced, adding that it was not clear what antibodies levels were sufficient.
Lau said real world data had proved that the Sinovac jab could ward off Covid.