Chief Executive Carrie Lam Cheng Yuet-ngor, meanwhile, said at her regular epidemic press briefing on Monday that further analysis was warranted in the future to ascertain the actual number of Covid-19 infections in the city.

That “grand total” might serve as a better baseline for determining the death rate, she said, citing suggestions from University of Hong Kong (HKU) infectious disease expert Professor Ivan Hung Fan-ngai.

“Whether it is 1 million, 2 million, 3 million or 4 million will make a lot of difference,” Lam said. “[But] for the time being, we will not move to that immediate adjustment. Otherwise, it would cause confusion.”

The city has one of the world’s highest fatality rates for the coronavirus, mostly among undervaccinated elderly residents.

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Based on the official tally of just over 1 million cases, the overall case fatality rate as of Sunday stood at 0.64 per cent, though that figure jumped to 9.35 per cent for people aged 80 or older.

According to the World Health Organization, the case fatality rate is the proportion of deaths among identified confirmed cases.

But the true level of transmission is often underestimated because infected people go undetected either because they are asymptomatic or only have mild symptoms.

Cases may also be misdiagnosed and attributed to other diseases with similar symptoms, such as influenza.

Pointing to findings from weekend lockdowns of four Tai Po public housing estate buildings, where a quarter of residents were found to have already been infected, Lam said the same proportion could apply to the overall population.

“Perhaps around one-fourth of the population has been infected,” she said. “When the epidemic has been stabilised, much public health data might need to be analysed and reviewed again.”

Still, Lam added, even if that many people had indeed contracted the virus, the total number of cases would still be lower than estimates by various experts, who have put the figure at anywhere from 2½ million to 5 million.

While arriving at an accurate count was “not easy”, she said, “we agree that the number of infections should be higher than the accumulated figure reported daily”.

She noted that a total of 16,710, or 10.5 per cent, of households had not answered their doors during the 287 overnight lockdowns of residential buildings that had been carried out since the fifth wave began in late December.

But Nancy Leung Hiu-lan, assistant professor in the division of epidemiology and biostatistics at HKU’s School of Public Health, warned of a selection or sampling bias by assuming the prevalence in a housing estate represented the whole of Hong Kong.

She said the 25 per cent figure at Tai Po’s Kwong Fuk Estate could be underestimated due to a self-reporting bias – those who were previously infected were not required to undergo testing during the lockdown operation.

HKU’s Hung, co-convenor of the government’s panel on adverse vaccine reactions, also said on Monday the government’s official count should not be used to calculate the case fatality rate, adding that as many as 4 million people were believed to have contracted the virus.

“In fact, the overall death rate of the pandemic in Hong Kong is lower,” he told a radio programme. “The death rate calculated [out of 4 million cases] is around 0.18 per cent, which is a bit higher than that of influenza each year.”

Separately, the Hospital Authority also found that the number of deaths directly caused by the coronavirus could be lower than the official record.

Authority chief executive Dr Tony Ko Pat-sing on Sunday said a preliminary analysis showed that more than 40 per cent of fatalities among Covid-19 patients had been caused by the disease, while over 30 per cent appeared to be unrelated.

He added that it was difficult to determine whether a link existed for the remaining percentage, as some people had died before or shortly after being admitted to hospital.

Dr Sara Ho Yuen-ha, a chief manager at the authority, on Monday said deaths in the fifth wave were reviewed by an expert panel composed of university professors and public hospital officials.

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They also looked at various factors including whether the patient was vaccinated, had underlying medical conditions and opted out of receiving cardiopulmonary resuscitation.

She added that other countries, including the United States and Singapore, had also reviewed how many patients had actually died of Covid-19.

Meanwhile, Shanghai on Monday started a four-day lockdown in two stages at Pudong and Puxi respectively in a bid to contain a rising number of Covid-19 infections.

Asked if Hong Kong could learn from Shanghai’s anti-epidemic measures, Lam said each city’s strategy depended on its own characteristics.

“There is a reference value of the work done in different places,” Lam said. “But what strategies are to be adopted by Hong Kong will depend on the city’s situation.”

She added: “Our anti-pandemic approach should allow us to connect to the mainland as well as overseas. This is a successful strategy. It is not easy but we should strive to achieve this.”

Monday’s press conference centred on the government’s efforts to ramp up the city’s capacity to store and cremate bodies, which has been taxed during the fifth wave.

Director of Health Dr Ronald Lam Man-kin said the capacity of public mortuaries had been increased from 1,350 bodies to 4,600 following the addition of spaces in various facilities.

He added that a hotline had been established for bereaved families to receive emotional support from the Department of Health’s clinical psychologists.

The “Covid-19 Grief Support Hotline”, which began operating from March 22, runs from 9am to 9pm every day until April 30. The helpline can be reached at 9814 1325.

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The number of time slots at the six crematoriums under the Food and Environmental Hygiene Department has also increased from around 140 a day to nearly 300.

The facilities were now operating almost around the clock, according to Director of Food and Environmental Hygiene Irene Young Bick-kwan.

As part of other relief measures to support Hongkongers, city leader Lam also said that 70 million rapid tests would be distributed to residents in anti-pandemic packages, which would be given out early next month.

So far, pandemic control resources worth more than 3 billion yuan (US$471 million), such as medicine and items for testing and personal protection, have been delivered to Hong Kong, according to Beijing’s liaison office in the city.

In a another development, the Social Welfare Department announced that to help hospitals and community treatment facilities prioritise manpower to handle patients with more acute clinical needs, new arrangements would be implemented to allow all respite centres to admit more infected elderly care-home residents with mild or no symptoms.

From Tuesday, when residents test positive, the care home can contact the department and the Centre for Health Protection directly for arrangements.

Meanwhile, upon the Hospital Authority’s referral, respite centres will continue to receive recovering elderly patients who are assessed as suitable for admission.

The city’s tally of confirmed cases currently stands at 1,136,192, while the total number of related deaths has reached 7,420.

Additional reporting by William Zheng and Danny Mok