In late 2021, Hong Kong stamped out the Omicron variant, making it one of the world's most formidable redoubts of zero coronaviruses.

A few weeks later, Omicron came again, this time causing an outbreak of cleaners at a public-housing estate that spiraled out of control. Since the emergence of the coronaviruses, the conflagration of resulting cases has killed people at a rate 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611 888-270-6611

Hong Kong's death toll per capita is no longer exceptional after the entire swine flu epidemic. Americans died from Covid at 90 times the rate of people in Hong Kong. The American toll was three and a half times higher by Monday.

As the United States braces for its own, less punishing rise in cases, and mainland China battles its biggest outbreak in two years, scientists have looked to Hong Kong for clues about the threat Omicron poses in an entirely different setting.

Health experts said several critical lessons emerged.

Scientists said that a broad swath of the population was important in the era of Omicron and BA.2. The top priority was inoculating as many older people as possible.

They said that the message was most pressing for China, where there is little immunity from infections earlier.

It was relevant again in the United States, where scientists are concerned about a potential surge of BA.2 cases because of subpar vaccination and booster rates among older people. Scientists don't expect the United States to face as serious a situation in the coming months as Hong Kong because of the number of Americans who have died from the coronaviruses.

Hong Kong's dreadful outbreak shows the perils of trying to eliminate the virus without a plan for what will happen next, health experts said. They said that Omicron's high transmissibility made it almost inevitable.

Hong Kong was left vulnerable by how few of its residents had immunity from previous infections because of tight restrictions and border controls.

A temporary isolation site to house patients with Covid-19 on Tsing Yi Island in Hong Kong.
ImageA temporary isolation site to house patients with Covid-19 on Tsing Yi Island in Hong Kong.
A temporary isolation site to house patients with Covid-19 on Tsing Yi Island in Hong Kong.Credit...Billy H.C. Kwok for The New York Times

Places that have low levels of immunity can be vulnerable to waves of cases as more contagious versions sneak in. The dean of medicine at the University of Hong Kong said that governments can still prepare for those waves.

Less than one-quarter of people aged 80 and over in Hong Kong had been given two doses of a vaccine before Omicron surged, compared with more than 90 percent of people in Singapore and New Zealand.

Scientists said it might be difficult to lift restrictions because of the number of unvaccinated older people in China. More than 85% of China's population have beenvaccinated. Zeng Yixin, a vice minister of the National Health Commission, said on Friday that less than 20% of people in the 80 and older age group have received a booster.

I don't think it's ready for the transition, according to Dr. Leung.

A number of Asian and Pacific countries had largely kept the virus at bay for two years, but had to face Omicron infections because the virus was so infectious. Many countries have avoided more devastating surges because of high vaccination rates.

Even though South Korea has recorded more deaths than the United States, the cumulative death toll per capita is still one-tenth of America.

Health experts said that Hong Kong's difficulties in vaccinating older people resulted from a combination of complacency and fears that older people and those in poor health were at risk of contracting the disease.

Almost two-thirds of young people in the city have been inoculated, but 39 percent of elderly people have not.

Many people in Hong Kong have been given the Chinese vaccine Sinovac, which appears to offer little protection from Omicron infections but a better defense against severe disease. The scientists said that getting shots to the most vulnerable is more important than the particular brand.

The elderly, especially those staying in elderly-care homes, are the problem in Hong Kong.

The United States has a high death rate for its older residents, but less than Western Europe. The United States is exposed to the same problem as booster shots become critical for shoring up protection against Omicron among older people. A majority of people over the age of 65 have not received a booster shot.

Scientists said that Hong Kong was not ready for its defenses to fail, unlike other parts of Asia.

Ben Cow said that the government had a strong fixation on zero Covid and that vaccination was not necessarily the priority.

Public health experts said that many older residents and their families adopted the same view. If Hong Kong's strict social-distancing measures and careful border controls were going to keep the virus out, was getting a vaccine worth the trouble?

David Owens, a family doctor in Hong Kong, said that telling people that the disease is never going to get in is less of an incentive to get vaccine.

People waiting to be tested for the coronavirus in Tsing Yi, which was placed under lockdown this month.
ImagePeople waiting to be tested for the coronavirus in Tsing Yi, which was placed under lockdown this month.
People waiting to be tested for the coronavirus in Tsing Yi, which was placed under lockdown this month.Credit...Billy H.C. Kwok for The New York Times

The University of Hong Kong's Dr. Cowling said that the city could have responded by either doubling the number of cases or by building better facilities for overseas arrivals.

Zero Covid is a good strategy if you can stay at zero.

Hong Kong eventually took steps to get older people to bevaccinated, once earlier inducements like vaccine passes proved useless. The government banned unvaccinated people from restaurants that serve dim sum in January. It was too late.

Hong Kong announced on Monday that it would lift some restrictions.

In the summer, Singapore began abandoning policies. It took a wave of the Delta variant to raise vaccination rates and disabuse people of the notion that they did not need protection.

Cases in Singapore have gone up, but deaths are low.

It's so much more transmissible that wearing a face mask helps, but not to the extent that it has impacted the epidemiology.

Some countries have succeeded while others have suffered from the Pandemic.

Scientists said that Japan has done a good job of containing cases during the Pandemic.

Early in the Pandemic, the country received sound public health advice from the government. Taro Yamamoto, a professor at the Institute of Tropical Medicine at Nagasaki University, said that residents took the advice seriously even though they were tired of precautions.

Most of the people in Japan have had their first vaccine. Even though the country is lagging in administering booster doses and had a surge of Omicron infections, death rates during Omicron have remained considerably lower than in nearby South Korea.

Professor Yamamoto said it was a mystery.