Medical experts on Saturday said that Hong Kong has already hit a target of 28 consecutive days without an untraceable Covid-19 infection – but are warning that rather than relaxing, Hongkongers should take this opportunity to prepare for a possible “fifth wave” of the virus.

Prominent University of Hong Kong microbiologist Yuen Kwok-yung, an adviser to the government on the pandemic, said investigations into suspected untraceable cases from earlier this month had discounted them.

“I do think we actually have achieved it,” Yuen said of the 28-day target signalling an end to the city’s fourth wave of coronavirus infections.

The Centre for Health Protection’s Chuang Shuk-kwan said the last local infection without a known source was therefore recorded on April 23.

But Yuen warned against complacency, saying “it’s perhaps just a matter of time before the fifth wave will come”, believing that the risk comes from new Covid variants.

He said Hong Kong should get its vaccination rate above 80 percent, test anyone with mild symptoms, and maintain its rapid contact tracing system.

People should continue wearing masks, incoming travellers should be fully vaccinated, and improvements must be made to indoor ventilation, Yuen said.

But Yuen also said that those who have been inoculated against Covid-19 should be allowed to go about their lives “more normally”.

“We should continue with schooling in ‘dual mode’ so those vaccinated would learn in school, and those unvaccinated would learn online,” he said.

He said eateries and entertainment venues should not have their operating hours shortened, as this was unfair to them and a lot of social activities would be affected.

He said vaccinated people should be able to go in at any time, even after midnight. But the unvaccinated should only be able to dine in at lunchtime, and be made to eat outside at other times.

Yuen said people who have been vaccinated should be allowed to isolate at home if their buildings require evacuation because of the vertical transmission of Covid-19. Those who have not been vaccinated should still be forced out of the building though, he said.

Asked why it has taken nearly six months for Hong Kong to come through the “fourth wave” of the coronavirus, Yuen said specific countermeasures at critical control points had not been instituted.

He cited the “dance cluster” as an example of people not following the rules, and reiterated the importance of maintaining mask wearing particularly in indoor settings.