Government pandemic adviser David Hui on Saturday said Hong Kong's daily Covid caseload is likely to remain in the low hundreds for several more weeks, adding that a major rebound in infections is unlikely.

"Judging by the recent number of cases [which] has been hovering around 250 and 300, I think the trend will continue for several weeks," the Chinese University professor of respiratory medicine said. The SAR reported 221 new local cases on Friday, in line with recent trends.

Hui said the increasing vaccination take-up and the fact that at least half of the population are believed to have been infected already should help prevent another outbreak, unless a new variant emerges.

But Hui noted that silent transmission of the Omicron subvariant BA.2.12.1 might be going on in the community, saying the four most recent cases weren't linked to the ones recorded previously.

The academic said the new subvariant was more transmissible than BA.2, which was common during the fifth wave of outbreak here, but it didn't seem to cause more severe symptoms.

Meanwhile, he said it was advisable for elderly people to get a fourth jab, though younger adults who were not at high risk of exposure to the virus could wait to see whether second-generation vaccines become available towards the end of the year.

"All the vaccine companies are conducting clinical trials, and the results won't be available so soon. But I guess by the last quarter of this year, more data will be available and some of the companies may be able to provide the second generation vaccine."