Why Social Distancing Could Go On A Lot Longer Than We Think
An influential report says Americans may have to stay home for months to keep coronavirus at bay. Here’s why.
If and when the world sees a reduction in the number of new coronavirus cases, we may have the work of Neil Ferguson, a British mathematical biologist, to thank. A widely respected epidemiologist, Ferguson has used mathematical models to study the transmission of swine flu, Ebola, Zika and other diseases. In early February, Ferguson and his colleagues at Imperial College London were among the first to conclude, using statistical analysis, that China had radically undercounted COVID-19 cases.
But it is a report that Ferguson released on March 16 that jolted governments in the U.S. and U.K. into action. If allowed to spread wholly unchecked, the disease would claim some 510,000 lives in Britain and up to 2.2 million in the United States, the study predicted (though it noted it’s unlikely any government would impose no control measures at all). Even with moderate levels of social distancing, the study warned, we’d see a surge of infections that would overwhelm hospitals and swamp health care systems.
Ferguson concluded that “intensive, and socially disruptive interventions ... most notably, large scale social distancing, will need to be in place for many months, perhaps until a vaccine becomes available.”
By week’s end, U.K. Prime Minister Boris Johnson had abruptly shifted course, after previously minimizing social distancing on the premise that large numbers of Brits would need to contract the disease to develop “herd immunity.” In the U.S., President Donald Trump discouraged gatherings of more than 10 people, and the state of California ordered all of its residents to shelter in place on March 19.
Ferguson and his colleagues had shared preliminary drafts of their study with British and American officials before they publicly released it. What else is in the report that so alarmed both Downing Street and the White House?
The Imperial College researchers predicted the ways that various interventions could slow rates of infection, hospitalization and death in the continued absence of effective medical treatments or a vaccine. The study looked at five interventions: home isolation of cases (staying home for a week if you have symptoms); household quarantine (where anyone who lives in the same house as someone with symptoms self-isolates for two weeks); social distancing (reducing contact with other people by 75%); social distancing of those over 70 (who are most at risk of dying after contracting COVID-19); and closing schools and universities.
Using data from China and other countries on how the virus is transmitted and how the infection progresses in patients, layered over models of social contacts in the U.K. and the U.S., the team created simulations to see how these interventions would work alone or in concert — and how they compared to no interventions at all.
All the interventions won out over complete inaction, and combinations of these methods were even more effective. But no one set of measures modeled in the simulations could stop the spread, save the most lives, and unburden an overwhelmed health care system all at once.
There’s More Than One Way To Flatten A Curve
You’ve probably seen some version of a graph representing potential COVID-19 cases with two curving lines on it. One line goes up real high, real fast, then comes back down; the other rises more gradually and doesn’t get as high, but takes much longer to return to zero. That second line is the “flattened” curve. That’s the goal.
If we were to let the virus spread unchecked, the number of cases would shoot up rapidly, and the influx of sick people would quickly overwhelm the capacity of hospitals. If, on the other hand, we implemented strategies to contain the spread of the virus — like practicing social distancing — it would pass from person to person more slowly, so there would be fewer cases at once, giving our health care system a fighting chance to respond.
That’s the basic picture. Of course, how to flatten the curve is an extremely complicated question. The Imperial College report modeled out the effects of two fundamental strategies — one set of interventions aimed at “mitigation,” or limiting deaths from the disease while still allowing some transmission, and one set aimed at “suppression,” or reducing the number of cases as much as possible. The researchers concluded that both approaches have the potential to flatten the curve, but neither is likely to stop the spread of the coronavirus any time soon.
Herd Immunity Could Limit The Spread Of Disease — But Not Enough
“Herd immunity” is a term that comes up every flu season (and in just about every anti-vaccination debate). It means that if enough people in a given population are immune to a disease, then the disease won’t be able to spread as easily from person to person. When it comes to diseases for which there are vaccines, like measles or the seasonal flu, that means a person who’s been vaccinated won’t get sick, and therefore can’t infect someone who hasn’t been vaccinated. And it means that if you do get sick, you won’t pass the infection on to people who have been vaccinated. Even when a vaccine isn’t perfect, it can still help to keep a disease from tearing through your town.
But we don’t have a vaccine for this coronavirus yet, because it is totally new to us. And because it’s totally new to us, people haven’t had the chance to build up natural immunity to it, the way most of us probably have some immunological memory of past flus (antibodies) that help us resist getting sick every year.
What if we gave the population time to build up immunity? That’s part of the thinking behind the mitigation approach. If we isolate the most vulnerable (older people and people with existing health conditions) and those who are showing symptoms, but we let healthy (mostly younger) people go about life ― possibly passing the virus around, but not feeling sick as a result ― those people will build up antibodies to the novel coronavirus, and eventually herd immunity will naturally hamper its spread.
The Imperial College report concluded that with a combination of social distancing just among seniors and isolation of people with symptoms of COVID-19 and those who live with them, we could “reduce peak critical care demand by two-thirds and halve the number of deaths” over three to four months’ time.
But there’s a “but”: “This will not be enough to prevent health systems being overwhelmed,” Ferguson said. Even in this “‘optimal’ mitigation scenario,” the report warns, the need for critical care would be eight times higher than what hospitals in the U.S. and the U.K. can handle. (Capacity is represented by the flat red line in the graph below.) And a lot of people would still die: 250,000 Brits and as many as 1.2 million Americans.
Imperial College London
Mitigation strategy scenarios for Great Britain showing critical care (ICU) bed requirements. The black line shows the unmitigated epidemic. The green line shows a mitigation strategy incorporating closure of schools and universities; the orange line shows case isolation; the yellow line shows case isolation and household quarantine; and the blue line shows case isolation, home quarantine and social distancing of those aged over 70. The blue shading shows the three-month period in which these interventions are assumed to remain in place.
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We’re Going To Have To Keep Up Social Distancing
The alternative to the mitigation route would be trying for suppression, to get the total number of cases as low as we can, which the Imperial College London researchers concluded “is the only viable strategy at the current time.” That means imposing social distancing to physically keep people from being able to pass the virus to each other. Millions of people in the U.S. and Europe are already getting a sense of what this is like. Get used to it.
“It’s not going to be a short-term process if we try to do suppression,” said Aubree Gordon, associate professor of epidemiology at the University of Michigan School of Public Health, who was not involved in the study.
According to the projections, to stop or significantly staunch human-to-human transmission in the U.S. or U.K. would require a combination of social distancing of the entire population, isolating known cases, and either quarantining the households of known cases or closing schools and universities.
Though they recognize that these measures would be “disruptive,” the researchers believe they would minimize the number of new cases enough to not overwhelm hospitals, so the sickest can be treated. “While there are many uncertainties,” the report acknowledges, “such a combined strategy is the most likely one to ensure that critical care bed requirements would remain within surge capacity.” (One of the uncertainties is what happens when health care professionals can’t get child care and have to miss work.)
There’s a “but” here, too. Social distancing prevents herd immunity from developing. As soon as isolation and social distancing restrictions are lifted, the coronavirus will start spreading all over again.
“The problem is that no one other than those who have recovered from the infection are likely to be immune,” Barry Bloom, an infectious disease and immunology expert at Harvard’s T.H. Chan School of Public Health, told HuffPost.
And since the whole point of suppression is that very few people will get it, that means very few will develop immunity. The herd could get hit hard once again.
Cases Of The Virus Could Go Down — And Then Go Way Back Up
According to the model, if the U.S. were to put social distancing measures in place by the end of March and enforce them for five months (yes, five whole months), you could expect to see infection rates decrease, or at least stay more or less within hospitals’ critical care capacity, until restrictions are lifted. After that, they would rise again, peaking sometime between October and December.
Imperial College London
Suppression strategy scenarios for the U.S. showing ICU bed requirements. The black line shows the unmitigated epidemic. Green shows a suppression strategy incorporating closure of schools and universities, case isolation and population-wide social distancing beginning in late March 2020. The orange line shows a containment strategy incorporating case isolation, household quarantine and population-wide social distancing. The red line is the estimated surge ICU bed capacity in the U.S. The blue shading shows the five-month period in which these interventions are assumed to remain in place.
This pattern may seem familiar. The flu tends to go down in the summer when it’s hotter and more humid and people are spending less time cooped up indoors. Then rates rebound in the fall. It’s possible that the novel coronavirus could behave similarly, though Gordon points out that it seems to be transmitting quite easily in hot, humid climates like Singapore and Indonesia. Scientists don’t know enough about it to make a prediction. A summer slump and autumn rise could have to do with seasonality of the infection — or it could be coincidental timing.
“No one really knows that this virus will survive the summer and come back in the fall,” Bloom said. “Everybody, including the model makers, are speculating.”
What’s pretty certain is that we won’t have a vaccine for a year to 18 months (or more), and that’s too long to keep people from going to work or school. What’s more, the better social distancing works, the worse things will be when the virus returns. “The more successful a strategy is at temporary suppression, the larger the later epidemic is predicted to be in the absence of vaccination, due to lesser build-up of herd immunity,” the report says.
That’s why the Imperial College model suggests that after an initial period of strict social distancing, people could start to move about again — until the number of COVID-19 patients in hospital ICUs rises to a certain level, at which point the restrictions would kick back in.
It might look like this: We spend April, May, June and July living a no-school, socially distanced existence, until critical cases fall dramatically. Then we get a few weeks’ reprieve before cases climb up to the trigger point and school is canceled again.
The “triggering” model is more nimble; the thresholds can be raised or lowered as trends change, or on a state-to-state basis. And it allows for periods of normalcy, although social distancing would be in effect two-thirds of the time. (Case isolation, household quarantine and social distancing of people 70 and over would remain in effect throughout.) And the number of cases would continue bouncing up and down until we found an effective vaccine. The researchers’ simulation goes for two years.
The Prospects Are ‘Scary’ ― But The More We Learn, The More We’ll Know
“The challenges we collectively face are daunting,” said Christl Donnelly, one of the authors of the Imperial College report, in a statement. “However, our work indicates if a combination of measures are implemented, then transmission can be substantially reduced. These measures will be disruptive but uncertainties will reduce over time, and while we await effective vaccines and drugs, these public health measures can reduce demands on our healthcare systems.”
“It’s a very well done study,” Gordon said, “and very scary.” But she emphasized that the model will be continually updated and refined as we learn more about the virus and how to treat it, and as we ramp up testing to see how it’s spreading here.
Policy and decision-making will depend on testing and “having really smart people model the course of the epidemic in real time, not just in analogy to China,” Bloom said.
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