University of Hong Kong's microbiologist Ho Pak-leung said on a Monday morning radio programme that collecting sewage from residential buildings and testing the Covid virus is no longer effective under the current epidemic circumstances.

"The sewage test sample from a building to indicate that hidden cases and block the building for isolation or Covid tests, had an important role in the early stages of the epidemic since it can help to locate the cases in a confined space," he said, "However, it is not necessary now as the cases reach around 10,000 every day."

He added that the government had accepted the possibility of infection inside buildings and considered the risk manageable by granting home isolation for confirmed patients.

"Authorities should concentrate on raising the vaccination rate, especially for the elderly," Ho said, noting the symptoms of Covid appearing in adults were similar to influenza.

Besides, Ho argued that the grace period between the second and the third dose of the Covid vaccine for people aged above 12 to receive should be reduced to five months, claiming it would contribute to increasing the vaccination rate.