By Umair Irfan 

Across the world, the omicron phase of the Covid-19 pandemic is now piling up towering case counts in places that have largely managed to keep the disease in check until this point. This troubling rise may signal that another wave of Covid-19 is rising in countries just coming out of their own omicron shadows, including the United States.

Hong Kong now reports the world’s highest death rate from the disease. Hospitals are overwhelmed and the surge is fueling a mental health crisis and leading to suicides, particularly among elderly residents.

Mainland China is also seeing major outbreaks in metropolises like Shenzhen and Shanghai, putting millions of people under lockdown and halting production in major international manufacturing centers. These outbreaks are testing China’s stomach for its zero-Covid approach to the pandemic, a costly but effective approach where entire cities grind to a halt to control outbreaks.

In South Korea, once hailed as a pandemic success story, case counts have broken a new record with daily reported infections topping 600,000.

Australia and New Zealand, which had previously held cases to enviably low levels, have also seen new spikes in recent weeks. The list goes on: Singapore, Thailand, Vietnam.

There are some common factors among these outbreaks. The biggest one is that the virus itself has changed. The mutations in the omicron variant of the virus that causes Covid-19, first detected in November 2021, make it the most contagious version of the virus known to date and allowed it to evade immunity — both from vaccines and from previous infections — better than other variants. Many of the earlier omicron waves were caused by a subvariant known as BA.1. Another omicron subvariant known as BA.2 is even more transmissible and is now driving a distinct spike in new cases.

However, there are also variables that make each of these outbreaks unique, namely how leaders in these regions deployed their public health strategies — testing, contact tracing, travel restrictions, vaccination — and when they relaxed them.

The good news is that most Covid-19 vaccines are just as protective against severe disease caused by BA.2 as they are against BA.1. And omicron causes a lower rate of hospitalizations and deaths among vaccinated people compared to other variants.

As the world enters the third year of the pandemic, these surges are a tough lesson about the perils of complacency. But for countries watching from afar that may be on the cusp of another round of infections, the latest series of outbreaks abroad also offer policy lessons on the best ways to dampen Covid-19’s worst effects.

How Hong Kong ended up with the world’s highest death rate from Covid-19

Hong Kong, a dense city of 7.4 million people, saw daily new Covid-19 cases climb above 66,000 this month. The per capita death rate reached 37 per million residents and one fatality per 20 infections, very high compared to rates among developed countries.

It’s a stark shift from how well Hong Kong weathered much of the pandemic, building on its experience with other coronaviruses like the 2003 SARS outbreak. Hong Kong has also maintained strict border controls. Visitors face a 14-day quarantine requirement with location-tracking wristbands, when they are allowed to enter the city at all. City health officials also maintained a robust contact tracing system.

As a result, Hong Kong went long stretches during the pandemic without any cases at all and with life largely continuing as normal.

“We had a period of about six months without a community outbreak of Covid in Hong Kong in the second half of 2021, but I think it was inevitable that an outbreak would occur sooner or later,” said Benjamin Cowling, chair of epidemiology at the University of Hong Kong’s public health school, in an email.

What’s changed now is that the BA.2 subvariant, which is driving the current wave of infections, is very, very easy to contract. Viruses like SARS-CoV-2, which causes Covid-19, are prone to mutation. The more people they infect, the more likely it is that they will change, and some of those changes can make the virus more transmissible, cause more severe illness, or better evade the immune system. (A variant is a category of a virus with a distinct grouping of mutations. But if two strains of a virus have only a handful of differences between them, they may be classified as subvariants like BA.1 and BA.2.)

BA.2’s reproductive number — how many other people each infected person goes on to infect on average — is around 10. With stringent public health measures like social distancing, frequent testing, and quarantining, the reproductive number dropped to 2 or 3, “which is a very substantial reduction, but not enough to prevent an outbreak from occurring,” Cowling said. As long as the virus’s reproductive number says above 1, it will continue to spread. But BA.2’s raging transmission also means that it quickly runs out of people to infect, leading to a sharp rise and rapid decline in cases.

Covid-19 vaccines have helped cushion the blow. More than 80 percent of Hong Kong’s population received at least one dose of a vaccine, and more than 30 percent have received a booster. Hong Kongers received Pfizer/BioNTech’s mRNA vaccine and Sinovac’s inactivated virus vaccine. The Chinese-made Sinovac vaccine was more popular among older adults, but it appears to be less effective than other vaccines against omicron. The current BA.2 is cresting months after the initial vaccine rollout, so some of the protection they provide is declining as well.

But Hong Kong’s vaccination rate is just 37 percent for people over the age of 80, one of the groups that is most vulnerable to severe Covid-19. The rate at which Hong Kong is vaccinating its elderly has fallen by 85 percent in recent weeks.

“Almost all of the severe cases and deaths have occurred in unvaccinated people, so it doesn’t seem that declining immunity is playing a major role,” Cowling said.

Why are older Hong Kongers not getting vaccinated as much? There are a number of factors, explained Hsiu-Hwang Ho, a retired philosophy professor living in the city.

“Their families are worried about the risks as there are rumours around, mistrust in government, government did not do well in the vaccination campaign (neither professional nor educative enough to convince people), government inertness in reaching out to the elderly with mobility problems,” Ho, 83, said in an email. He recently tested positive for Covid-19, though he received the Pfizer/BioNTech vaccine after being convinced by his daughter, a doctor.

Another factor in Hong Kong’s outbreak is that its earlier successes may be working against it now. By keeping cases down, there are fewer people with immunity acquired through infection with SARS-CoV-2. “Therefore those people who are unimmunized are vulnerable, and there are more of them in a place like Hong Kong than here because of the lack of prior infections,” said William Hanage, an associate professor of epidemiology at Harvard University, in an email.

Though cases and deaths are rising, they are far lower now than they would have been earlier in the pandemic

Many of the forces driving Hong Kong’s Covid-19 outbreak are also playing out in other countries like South Korea, which did well earlier in the pandemic, but are seeing spikes in cases now. Dampening earlier waves of infection left people in some areas more vulnerable to future outbreaks. Since fewer people were infected in these countries, fewer people acquired immunity to Covid-19. This is a good thing because preventing the virus from running rampant avoided an enormous death toll, but it makes vaccination all the more critical.

Otherwise, people who were neither vaccinated nor infected by a prior strain are now facing the most dangerous or contagious variants of the virus with immune systems that have no experience with SARS-CoV-2.

One caveat is that while the vaccines do a good job of preventing people from ending up in the hospital, they aren’t as effective at preventing infections. Many SARS-CoV-2 infections produce mild symptoms or none at all, which can allow the virus to spread undetected. So countries need a combination of vaccinations plus other public health measures to keep a lid on Covid-19 cases.

“Given the limited effectiveness of vaccines against omicron ‘infection,’ the room for community spread or population susceptibility could be quite high, compared to other countries that had experienced a large surge in the previous months,” said Young June Choe, a clinical associate professor of pediatrics at Korea University Anam Hospital, in an email.

As for why the cases are surging now, that is partly a function of the recent emergence of BA.2, but also because governments are starting to relax.

“International-travel quarantine measures were enforced, and the new social distancing had been in place in December 2021 through January 2022, which are now getting loosened after all,” said Choe.

While the rise in new Covid-19 cases and deaths is worrying, Choe notes that many of these countries show how a successful “flatten the curve” public health strategy can play out. By taking aggressive measures to limit infections, South Korea, Hong Kong, New Zealand, and others prevented their hospitals and clinics from being overwhelmed.

“They’ve managed to flatten the curve through the whole pandemic, and that’s probably helped with taking the burden off their health care system and reducing overall mortality,” said Davidson Hamer, a professor of global health at Boston University.

That helped ensure there were enough beds, doctors, and nurses to treat Covid-19 patients while also meeting other routine health care needs. These regions also bought themselves time to distribute vaccines that drastically reduce the chances of being hospitalized with Covid-19. So even though cases are spiking now, they’re far less deadly than they would have been earlier in the pandemic.

South Korea, Australia, New Zealand, and Singapore are reporting case fatality ratios — the number of deaths per 100 confirmed Covid-19 cases — of just 0.1 percent or less, compared to 0.8 percent in the United Kingdom and 1.2 percent in the US.

“In short, the main purpose of public health measures in S. Korea was to minimize death, and the statistics still meet the goal,” Choe said.

The recent rise in infections did push back plans in South Korea to reopen businesses like gyms and hair salons, and many countries facing spikes snapped back limits on gatherings and travel. It’s not clear, however, how much of an effect such tactics will have at this point.

Taken together, these outbreaks show that Covid-19 vaccines are a powerful tool for reducing the harm of the disease, but they work best in concert with a suite of public health tactics for controlling infection.

The United States should pay close attention

The United States is coming out of its deadliest phase of the pandemic and new Covid-19 cases are dropping sharply from their winter high. But more than 1,000 people in the US are still dying every day from the disease. Meanwhile, much of the country is relaxing requirements to wear face masks, testing is declining, and Covid-19 vaccination rates are leveling off. The US has not seen a wave of infections fueled by BA.2 just yet, but one may be looming. Western Europe is now starting to see another wave of infections and, throughout the pandemic, a rise in US cases has followed behind.

“It’s inevitable that we’re going to get some level of resurgence,” said Roger Detels, a distinguished research professor of epidemiology at the University of California Los Angeles.

That countries with robust pandemic Covid-19 policies are seeing a tsunami of infections is not a reason to give up. A strong public health response led by vaccinations can prevent a great deal of suffering.

Yet the White House is warning that it will run out of money for Covid-19 vaccines, treatments, and surveillance without a cash infusion from Congress. Surveillance is particularly important for tracking BA.2. While conventional Covid-19 PCR tests can detect the subvariant, many of them can’t distinguish it from other variants like delta, so health officials may be missing crucial signs of a looming wave. Keeping track of BA.2 requires genomic surveillance, which is a more involved process than simply testing for the virus. The US’s genomic surveillance capacity has improved in recent months, but reporting and coordination remain spotty.

US health officials are also increasingly looking at wastewater surveillance as an early warning sign of a Covid-19 outbreak.

How severe the next Covid-19 wave will be also hinges on how much the public is willing to take precautions, and many people are already putting masking and social distancing behind them. But as the pandemic has shown over and over, Covid-19 sets its own schedule.