As China virus cases near zero, experts warn of second wave
China has no new infections of the coronavirus domestically for the first time since the start of a crisis that has sickened over 80,000 Chinese people. But what could be a sign the country has defeated the fatal pathogen is likely to just be a temporary reprieve.
While the outbreak's epicenter has shifted to Europe, where there are now more cases being reported daily than at the height of China's crisis, epidemiologists warn that the Asian giant could face subsequent waves of infections, based on patterns seen in other pandemics.
The nature of this particular virus also raises the risk of a resurgence. The coronavirus is harder to detect and lingers longer than the one that caused Severe Acute Respiratory Syndrome in 2003, which infected 8,000 people before fading out. That will make future waves of the new pandemic more difficult to prevent.
As other countries wrestle with how far to close down civic life, they'll be watching China, where the virus first emerged last December, to see what happens when it lifts the harsh lockdowns and social distancing measures that have helped curb the its outbreak.
There were no new cases reported Thursday in Wuhan, the city in central Chinese Hubei province from which the outbreak began. There have been no new cases in the rest of the country for seven days, a dramatic plunge from the height of an outbreak that killed more than 3,000, and caused a historic economic contraction.
China's measures -- which included a massive quarantine of Hubei province, a region of 60 million people -- had success in interrupting transmission in the rest of the country, said David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine.
"The concern is what will happen after they end these measures."
Even if there had been many times more coronavirus cases than officially reported by the Chinese government, less than 1% of the population would have been infected in its first wave, "leaving most people in China susceptible," said Raina MacIntyre, a biosecurity professor at the University of New South Wales in Sydney.
"The global pandemic will not be contained until we have a vaccine, or most of the population is infected," she said.
For now, the Chinese government is focused on cracking down on "imported cases" as infections in travelers entering China outnumber domestic cases, according to data from the National Health Commission. The country has stringent control measures in place to ensure that "if the virus pops back up, it will be addressed rapidly," said Rebecca Katz, director for the Center for Global Health Science and Security at Georgetown University.
In Beijing, where authorities have confirmed 54 infections among travelers, all inbound visitors must now spend 14 days after arrival in specified quarantine locations, the cost of which they must foot themselves. The Chinese capital is also likely to order flights to stop in nearby cities to test passengers before they can journey on to Beijing.
Financial hub Shanghai and manufacturing center Guangdong are also tightening restrictions.
"It's going to keep burning. The virus is still out there," said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "We expect it to leak back in from the rest of the world."
And while China has officially stated that it believes the peak of the current outbreak is over, its top scientists are still struggling to predict how the virus will behave from here.
"No one knows whether the virus will disappear ultimately, or will it persist like flu and become prevalent intermittently, or will it be like hepatitis B that resides in people without sufficient immunity and spreads to others in that way?" said Wang Chen, the dean of Peking Union Medical College, in an interview with Xinhua on Friday.
He called for serological testing -- which identifies antibodies in a patient's blood to see if they've been exposed to the virus -- to monitor how immunity is generated so as to understand the pathogen's transmission patterns.
Beyond the challenges of stopping a pandemic in an inter-connected world with frequent travel, many researchers have already concluded that it will not be eliminated like its cousin that caused SARS.
In the early days of infection, when people have not yet developed symptoms to realize they are sick, high amounts of the virus are already present in their blood and they are transmitting it to others, said John Mackenzie, an emeritus professor of infectious diseases at Curtin University in Perth, Australia.
Early on in an infection, it's also possible that a person could test negative even if they have the virus, according to the Centers for Disease Control and Prevention.
These stealthy qualities make complete elimination difficult, if not impossible, without a vaccine -- a product that drugmakers have said will take until next year to develop.
Very different factors were at play in the SARS pandemic, where those who were infected weren't contagious until they were visibly very sick. That's also the case for viruses that cause Ebola and MERS.
"With SARS, there was no transmission during incubation or during the early symptomatic phase, and so control was relatively easy once we knew the transmission dynamics," said Mackenzie.
Isolating sick patients ultimately arrested transmission, and health authorities were able to stamp out the pathogen without a vaccine or cure being developed. Ebola and MERS also do not spread easily, and most infections occurred through contact with the virus's animal host or in hospitals when caring for infected patients.
In contrast, the pandemics that began in 1889 and 1918 -- caused by influenza viruses that had similar levels of contagiousness to the coronavirus -- had three waves of infections, with the later waves more lethal than the first.
In 1918, three waves hit in quick succession within the space of a year, with the latter two waves accounting for most of the 50 million total death toll.
While researchers do not know for sure why later waves were more deadly, a phenomenon known as "antigenic drift," in which small, natural changes build up in a virus's genetic make-up over time, can change the pathogen enough to make it more harmful to human beings.
"This coronavirus is more comparable to influenza," said Ben Cowling, a professor of epidemiology at Hong Kong University, who said it might take two months for fresh cases to emerge in China. "It spreads too easily, and most parts of the world don't have the ability like China to do containment and control to get rid of it."
The U.S. and European countries are focusing now on trying to "flatten" the curve -- spreading out infections over a longer time period to reduce the strain on the health system. What containment will look like in the long term depends on what we learn about the virus, said Dorit Nitzan, coordinator of health emergencies for the WHO's European office.
She cautioned against counting on protection from herd immunity -- when the majority of a population is no longer susceptible to a virus because they've either been vaccinated or have already contracted it and recovered -- as there are still too many unknowns.
"It's a new virus, and we have to learn it," Nitzan said in a press briefing on Tuesday. It is still unclear how long patients who recover will be immune, or whether the virus will change frequently like the seasonal flu, she said.
In one of the first studies to model the dynamics of the coronavirus once the current pandemic is over, a team from the Harvard T.H. Chan School of Public Health projected that future outbreaks will probably recur in the wintertime. This finding was based on factors like seasonality, the duration of immunity and the strength of cross-immunity to and from other human coronaviruses.
With some breathing space for now, China must pivot from fighting the virus to finding a way to live with it.
"The virus is constantly growing and changing, which makes total containment impossible," said Chan Kung, health policy analyst at Beijing-based consultancy Anbound, who advised the local government during the SARS outbreak. "The only way to go forward is to understand it, adapt to it and make sure the virus doesn't cause dramatic outbreaks so that the existing healthcare system can handle it."
— With assistance by Dong Lyu, Naomi Kresge, Claire Che, Jeremy Diamond, and John Lauerman