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Back in the middle of March, lockdowns were advertised as a way of "flattening the curve":

As the spread of the coronavirus continues, everyone from the medical community to government officials is talking about "flattening the curve." What does it mean, exactly? The "curve" here refers to the line on a graph that rises as the number of cases of a particular infectious disease increase, then falls as that number goes down. Flattening that line means slowing transmission of COVID-19, the illness caused by the new coronavirus, so a community or society doesn't end up with an overwhelming number of cases all at the same time.

But at some point the conversation has shifted - countries are talking about implementing contact tracing to eradicate the virus altogether, rather than merely reducing the hospital load. This had been used as a justification against immediate reopening, such as this example from California:

California Gov. Gavin Newsom (D) said Wednesday that the state is planning to train up to 10,000 contact tracers amid the coronavirus pandemic.

Expanding contact tracing and testing is one of six indicators Newsom said last week would drive the state's decision to gradually modify portions of the stay-at-home order.

What has been the reason behind this shift in attitudes? Some possible explanations I have out of the top of my head:

  1. We now have better information about the virus lethality. This is true, but the information we have points at lower mortality, not higher. Back in March the WHO has been claiming a mortality rate of 3.4% and a hospitalisation rate of 20%. However as per NYC serological studies, the true IFR is somewhere around 0.5% and the true hospitalisation rate is somewhere around 2%.

  2. The success of other countries (South Korea, New Zealand, Iceland) emboldened others. This is true, but other countries were already quite successful at eradicating the disease by March. Namely China and Taiwan.

  3. Countries want to avoid the staggering death rate of herd immunity. This is true, but shouldn't have this been the case from the beginning given that initially a 3.4% death rate was projected?

  4. Politicians wanted to eradicate the virus from the beginning, but needed to use "flatten the curve" as a short term solution. This would explain it, but would require better proof than my conjecture.

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    Your second quote doesn't seem to mention eradicating the virus altogether? – tim May 4 '20 at 8:36
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    Likewise, I have heard nothing to suggest governments are now aiming to eradicate the virus. Indeed the message I have heard has been "this is here to stay guys". Have you anything to support the premise of your question? – Dan Scally May 4 '20 at 8:38
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    @DanScally states refusing to reopen despite having hospital capacity is the biggest indicator. – JonathanReez May 4 '20 at 8:45
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    @JonathanReez That doesn't follow in the slightest. Not wanting to saturate (as distinct from overwhelm) your health care system does not imply that you think you can eradicate the virus at all. If there's nothing to support the premise, I would challenge the validity of the question. – Dan Scally May 4 '20 at 8:48
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    @JonathanReez the quote (or the article) doesn't mention herd immunity either though? – tim May 4 '20 at 8:49
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While I agree with the comments that California is probably bad as an example of a "shift to eradication", New Zealand has moved in this direction.

“We have the opportunity to do something no other country has achieved—elimination of the virus,” Jacinda Ardern, the country’s Prime Minister, said Apr. 16.

As for what caused that (NZ) shift or actually made it possible in the first place...

Michael Baker, a professor at the University of Otago’s Department of Public Health who advises the government on its COVID-19 response, tells TIME that “an ability to control entry points” is a key feature of the elimination strategy. [...]

“New Zealand has an advantage of a relatively isolated location, which meant fewer early travelers from China and other infected areas and a longer time before cases started to appear. New Zealand saw its first cases on Feb. 28, at a time when the U.S. already had community spread and likely thousands of unreported cases,” says Thomas J. Bollyky, the director of the global health program at the Council on Foreign Relations. [...]

New Zealand’s low population density also means it may be harder for the virus—which is transmitted via close contact and airborne respiratory droplets—to spread. Only 1.66 million people live in Auckland, New Zealand’s biggest city, and its population density is less than one twentieth of America’s biggest urban center, New York City.

Bollyky also says that New Zealanders had the advantange of more homogeneous healthcare system, higher trust in government, and more law abidance in their society.

Testing-wise the US and New Zealand haven't that far apart though 2,190 in NZ per 100,000 inhabitants vs 1,420 in the US, according to that Time article.

On the other hand, the article also argues that [other]:

Experts argue that the price of New Zealand’s strategy is extremely high. [...]

Proponents of the elimination strategy acknowledge the economic hardship it has caused, but they say that it will allow the country to restart its domestic economy faster and avoid the pain of a long cycle of lockdowns as cases surge and are brought back under control. “It’s brutal for the economy, but the huge benefit is that you have an exit strategy,” says Baker. He adds that since travel has stopped across the world, the damage to New Zealand’s economy was going to happen no matter what. “It’s not like suddenly international tourism and cruise ships are all going to start up again,” he says.

So basically, if it looks like tourism is already dead for a while anyway from the supply side...

Their Treasury doesn't forecast a full economic recovery from Covid-19's [after]effects until 2024.

New Zealand seems to be in some kind of discussions with Australia for a "trans Tasman travel bubble":

"I can't see international travel occurring anytime soon, the risks there are obvious," Mr Morrison said. "The only exception to that … is potentially with New Zealand, and we have had some good discussions about that."

"There are significant advantages to New Zealand in terms of a trans-Tasman bubble not only [in terms of] domestic tourism, but equally we have a flow of people travelling between both countries, for business purposes, trade and so on," Ms Ardern said.

Ms Ardern said not to "expect this to happen in a couple of weeks' time," and said that she and Mr Morrison had a "very similar perspective of the type of timeline" involved.

While Australia has managed to control the outbreak better than many countries, they haven't managed the same feat as NZ yet. Morrison said about a week ago that Australia was "not in eradication mode". The Australian government is pushing hard for its residents to voluntarily download a "CovidSafe" phone tracing app.

Although they don't seem to publically acknowledge it [much], a lot of Western countries indeed seem to be eyeing the South Korean experience (with the drive for contact tracing), which in some ways has been more remarkable:

On Apr. 15, some 29 million people turned up to vote in parliamentary elections—yet no known infections arose, thanks to strict social distancing at the polls. On Wednesday [Apr. 29?], South Korea had zero local infections for the first time since the outbreak was first recorded 72 days previously (though four new cases had been imported.) “This is the strength of South Korea and its people,” President Moon Jae-in said on announcing the news.

South Korea’s health and welfare minister Park Neung-hoo explained to TIME exactly how his nation engineered such a remarkable turnaround. [...]

How did you resist the urge to impose more draconian containment measures like in China or other countries?

We never considered a full lockdown as part of our policy response to COVID-19. Although there was an explosive new outbreak in a certain region, we had confidence that we could locate contacts and isolate them successfully.

Although when you still have thousand+ new cases per day as California currently has, the SK experience is probably a rather distant target.

South Korea had set some clear goalposts for their transition to the current phase:

“Our war against the coronavirus has yet to end and it will not in the short term,” Prime Minister Chung Sye-kyun said at meeting with top officials on virus responses on Monday [May 4].

“Now we have to accept life with the coronavirus. We are facing the task of making a new life with this persistent threat of the virus.”

On Wednesday, Korea, which reported the first COVID-19 case on Jan. 20, will introduce a new regime in its fight against COVID-19 called “routine distancing.” [...]

Due in large part to the rigorous social distancing campaign, Korea, which reached a peak on Feb. 29 with 909 new cases, had managed to flatten the virus curve. It reported eight new cases Monday [May 4]. [...]

There were two conditions that had to be met for the country to switch to routine distancing: The country had to have fewer than 50 new infections per day, and the sources of infection had to be traceable in at least 95 percent of cases.

The conditions have been met.

Now, Korea seeks to build a post-coronavirus new normal where each individual is responsible for taking quarantine measures in their daily lives to minimize the risk of infection, which the government labeled as “everyday life quarantine” scheme.

The “routine distancing” guidelines detail how citizens should behave in specific places and situations to prevent the spread of the coronavirus — from workplaces and public transportation to hotels and shopping malls.

Common rules include: taking three to four days off from work when people don’t feel well, refraining from going outside when having fever higher than 37.5 degrees Celsius or when they are just back from a trip overseas, wearing a mask, washing hands for 30 seconds, ventilating a residence more than twice every day and keeping a 2-meter distance from others.

Note that it took South Korea about two months (or 1.5 if you want to consider that they went under 50 new cases/day mid-April) from the peak of nearly 1,000 new cases per day in Feb to "routine distancing" an handful of new cases per day (May).

However, given the test positivity rate differences between the US and South Korea, some doubt a similar strategy is feasible in the US anytime soon; from a mid-April article...

The test-positivity rate, then, is a decent (if unusual) proxy for the severity of an outbreak in an area. And it shows clearly that the U.S. still lags far behind other countries in the course of fighting its outbreak. South Korea—which discovered its first coronavirus case on the same day as the U.S.—has tested more than half a million people, or about 1 percent of its population, and discovered about 10,500 cases. The U.S. has now tested 3.2 million people, which is also about 1 percent of its population, but it has found more than 630,000 cases. So while the U.S. has a 20 percent positivity rate, South Korea’s is only about 2 percent—a full order of magnitude smaller.

South Korea is not alone in bringing its positivity rate down: America’s figure dwarfs that of almost every other developed country. Canada, Germany and Denmark have positivity rates from 6 to 8 percent. Australia and New Zealand have 2 percent positivity rates. Even Italy—which faced one of the world’s most ravaging outbreaks—has a 15 percent rate. [...] New York City’s positivity rate is an astonishing 55 percent.

Note that Australia and New Zealand are much closer to South Korea in that (test positivity) regard. So it may turn out that a "herd immunity" situation is going to happen in places like NYC instead... whether they planned for it or not. (An antibody survey of a sample population from NYC [published in May] found that 12.3% probably had been infected, with that percentage reaching some 27% in the Bronx and 25% among Hispanics or Latinos. So that's less than deduced from PCR test positivity by a factor of 2 to 4. One should also keep in mind that antibody surveys themselves have been mired in some level of controversy, at least the smaller scale ones conducted in California and Heinsberg, Germany, in particular because of how the samples were selected. I don't know if the larger and more recent NY survey had been criticized in a similar fashion or not.)


Actually, rather than eradication, some countries e.g. Germany, seem to just aiming for an R of about 1, which basically would keep the problem "in check" for as long as it needs to be (e.g. until a vaccine is developed etc.) but note that this approach is sensitive to the current number of infections, as a higher number allows less headroom (e.g. wrt to intensive care) should a sudden burst of cases happen.

Lars Schaade of the Robert Koch Institute (RKI) said only if the R value rose above 1.2 or 1.3 for several days would he be worried.

He also said that the fewer the overall number of infections, the greater the impact of an outbreak - like those recently reported in slaughterhouses - on the R value. [...]

If that rate goes above 1, the outbreak can escalate because anyone infected can pass the virus to more than one other person. But that is not the whole story.

What also matters is the actual scale of infection - the numbers of people catching the virus.

So in Germany, while the R is now slightly above 1, and may go higher, the authorities are concerned but not panicking.

That's because it's estimated that fewer than 1,000 Germans are becoming infected every day.

So even if the rate of spread accelerates, the problem can be handled with careful surveillance and mass testing, because the numbers involved are manageable.

By contrast, it's thought that in the UK something like 20,000 people are becoming infected every day - far fewer than at the height of the outbreak, but still a serious number.

And at that scale of infection, even a small rise in the R rate could have a dangerous impact [...]

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My answer specifically relates to the UK, but I presume this holds in many other European countries. The focus has shifted from flattening the curve because the curve has been flattened, at least for the initial peak. In his first speech outside No. 10 since recovering from the virus, on April 27th, Boris Johnson said:

I ask you to contain your impatience because I believe we are coming now to the end of the first phase of this conflict, and in spite of all the suffering we have so nearly succeeded; we defied so many predictions, we did not run out of ventilators or ICU beds, we did not allow our NHS to collapse, and on the contrary, we have so far collectively shielded our NHS so that our incredible doctors and nurses and healthcare staff have been able to shield all of us from an outbreak that would have been far worse.

We collectively flattened the peak, and so when we are sure that this first phase is over, and that we are meeting our five tests: deaths falling, NHS protected, rate of infection down, really sorting out the challenges of testing and PPE, avoiding a second peak, then that will be the time to move on to the second phase in which we continue to suppress the disease and keep the reproduction rate, the r rate, down, but begin gradually to refine the economic and social restrictions and one by one to fire up the engines of this vast UK economy.

This can also be seen from the graph of deaths in the UK:

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Clearly, the curve of deaths for the initial peak has indeed been flattened. The focus now moves onto reducing lockdown controls to ensure that the economy can recover, in order to prevent secondary causes of death and illness as a result of, for example, socioeconomic inequality. The only way to do this is with a vaccine, or which extensive contact tracing and testing. Clearly a vaccine will take a long time to produce and test for effectiveness and safety, so the remaining solution is the one you identify.

The reason that this was not the strategy from the start was that testing facilities just weren't there at the beginning of the pandemic - the UK only just met its 100,000 test per day target at the end of April, and trials are only just underway for the NHS contact tracing app.

So the focus has shifted in a way, but not really due to any new discoveries about the disease - merely that the initial curve is seen to have been flattened, and the focus is now on ensuring that a second curve does not rear its head, while also relaxing lockdown conditions.

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