If you want to know how long social distancing will interrupt the American workforce as you know, ask an epidemiologist. The answer, of course, is: it depends, as duration could be curtailed or extended depending on how the U.S. responds.

“If you suppress the epidemic your population is still susceptible,” Penn State epidemiologist Maciej Boni explained Thursday on Yahoo Finance’s The First Trade.

There’s a difference between suppressing a disease and establishing so-called herd immunity, according to Boni. Herd immunity occurs when enough people are exposed to the disease, overcome it, and develop immunity, either through person-to-person transmission, or through vaccination, making it difficult for a disease to spread.

If we don’t establish herd immunity, a second wave in the U.S. could happen over the 2020-2021 winter, Boni said. “It might start in October or November when the school gets back into session and it probably means 12 months of hardship for all of us,” he said.

Three timeline scenarios could play out

As countries around the globe have already shown, there’s more than one recipe to wrestle COVID-19. Some are comparatively swift and absent a vaccine leave populations vulnerable to a punishing second round of health and economic turmoil. Others lag and simultaneously breed risk of increased death as well as potential to inoculate masses from its future viral wrath.

According to Boni, three timeline scenarios could play out, and they depend in part on a population’s approach to controlling its spread.

One is the scenario that unfolded in China and South Korea where early quarantine and extreme social distancing measures suppressed the virus within about a month. While effective for quickly reducing person to person spread, the method falls short of protecting a population from a second wave, according to Boni.

View photos A surgical mask is placed on The "Fearless Girl" statue outside the New York Stock Exchange on Thursday, March 19, 2020, in New York. Stocks are swinging between gains and losses in early trading on Wall Street Thursday, but the moves are more subdued than the wild jabs that have dominated recent weeks. (AP Photo/Kevin Hagen) More

“We don't know what the endgame is, because when you lift the suppressive measures, the virus will come back,” Boni said.

A second scenario is where the virus transmits successfully during the summer, meaning enough of the population contracts and overcomes the virus to establish herd immunity — which Boni says could happen as early as late fall — so that it will cease to again threaten at pandemic levels.

Under a third scenario, the virus fails to transmit successfully during the summer, and like scenario one, continues to rear its head. Under both the first and third possibilities the rate of transmission hopefully slows enough to buy the healthcare system and its workers adequate time to develop a vaccine or treatment, and to fortify hospitals and treatment facilities to handle resurgence.

“It's like looking at the first 60 minutes of a hurricane and saying it's almost over,” Boni said. “It's not almost over at all. If the virus can transmit in the summer — under scenario 3 — we'll see an epidemic wave that lasts through the summer and possibly through the end of the summer.”

The best-case scenario with social distancing

Dr. Karen Edwards, professor and chair of University of California’s epidemiology department, told Yahoo Finance that the number of new COVID-19 cases would need to remain at zero for 14 consecutive days before any consideration to relax social distancing practices and send Americans back to work. The challenge, she, said is getting all Americans to adopt cohesive social distancing practices that can accomplish the two-week goal.

“The recommendations and guidelines about social distancing have been very patchwork across this country and there are probably some places that are not even really doing this at this point, so that's just going to prolong things,” Edwards said.

All Americans need to participate in social distancing on a national level to get transmission under control, she said. In a perfect scenario, she said, if everyone in the U.S. immediately adopted aggressive social distancing measures it could theoretically take two weeks to see the first day of no new cases. Under a best case scenario, that means social distancing practices could be relaxed in a month.

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