The key to ending the COVID-19 pandemic lies in expanding vaccination among the elderly and vulnerable groups, as well as ramping up preparedness of local medical systems against potential outbreaks, a renowned infectious disease expert said on Thursday.

"The case fatality rate (the ratio of deaths to diagnosis) of COVID-19 is an important indicator of whether a country can exit the epidemic. Amid Omicron outbreaks, the rate should be given even higher attention," Zhang Wenhong, head of the infectious disease department at Fudan University's Huashan Hospital, said during this year's Boao Forum for Asia in Hainan province.

Zhang said that although the pathogenicity of Omicron has markedly decreased from previous dominant strains, this variant is far more contagious.

"In such a circumstance, if a region's healthcare system is sufficient to tackle surging infections and take good care of the most vulnerable groups, such as the elderly and those with underlying illnesses, then we can save their lives as much as possible and maintain the fatality rate at a very low level," he said.

Meanwhile, vaccination coverage among these groups should also be stepped up, so as to strengthen their immunity against the disease and lower the rate of mortality, he added.

During the fifth wave of COVID-19 outbreak in Hong Kong, Zhang said, 90 percent of those who died had underlying illnesses and their median age was 86.

"More importantly, we found that a booster shot can provide significant protection and lower the rate of fatality," he said.

In Singapore and New Zealand, where immunization coverage among the elderly has exceeded 90 percent, COVID-19 fatality rates have dropped greatly.

"It is now vital to strengthen education on vaccination and increase accessibility, such as providing door-to-door services," Zhang said.

As of Wednesday, Shanghai had registered 25 COVID-19 deaths out of over 400,000 infections, according to Zhang. The city reported 11 more deaths for Thursday.

Zhang said that about 90 percent of the 25 mortalities were aged above 75 and nearly all of them had been diagnosed with chronic illnesses. "In the meantime, nearly all severe cases are unvaccinated."

More evidence has emerged recently to prove the value of vaccinations and booster shots.

On Thursday, a new study published by Chinese researchers found that people fully vaccinated with domestic, inactivated vaccines were at significantly lower risk of developing moderate or severe diseases.

The study is based on 27,000 cases recorded in Jilin city in the northeastern province of Jilin between March 3 and April 12. It was published in China CDC Weekly, the national public health bulletin and academic platform established by the China CDC.

Results show that unvaccinated or partially vaccinated people were about 1.8 times more likely to suffer moderate infections, nearly 9.5 times more likely to become severely ill and about 2.9 times more likely to become critically ill than fully vaccinated groups.

Compared with those who have received a booster shot, the unvaccinated or partially vaccinated were at even higher risk of developing mild or severe infections, according to the study. The same trend was also observed among people aged 60 and above, it said.

"Preliminary protective data on COVID-19 here is strong enough to indicate the public significance of the strategy of full vaccination and boosters, particularly among the older population, which is at markedly higher risk of critical and fatal outcomes," the study said.

It added that repeated booster shots, either using the same vaccine as initial injections or different vaccines, may be an effective measure for dealing with the epidemic in the future.

Zheng Zhongwei, head of China's vaccine development task force, also said on Thursday during the Boao Forum that three domestic vaccines tailored to ward off Omicron infections have entered clinical trials.

"If they meet requirements, we believe these Omicron-targeted vaccines will be launched in the market in the near future," he said.