The Hospital Authority (HA) said on Saturday that less than a third of its full time workers had had a Covid-19 jab.
Speaking on a radio programme, the authority's chairman Henry Fan said around 24,000 staff members had been vaccinated, with around 70% opting for the BioNTech jab. He said this was in spite of the authority offering half days off and shuttle buses to vaccination centres.
Last month the HA announced that front-line medical workers, who had not been vaccinated, should have rapid Covid tests on regular bases.
The authority's chief executive Tony Ko said on the same programme that the relatively stable pandemic situation here might be the reason. But he warned that the vaccines had a limited shelf life
"Of course we know some of the vaccines - in particular in Hong Kong, the BioNTech - they've got a limited time when the vaccines are more effective. So I think it is very important that both the public, and of course our colleagues as well, receive the vaccination as soon as possible," he said.
Government figures show that just over 17% of Hong Kong's population has received at least one Covid vaccination.
Experts estimate about 70% of a population needs to be immune to Covid, either through vaccination or recovery, to prevent transmission and stop the pandemic.
But this herd immunity depends on the infectiousness of disease. The World Health Organization says for highly infectious illnesses, like measles and polio, herd immunity is about 95% and 80% respectively.