So, here we are.

Pretty much nobody’s going to school on Monday, thousands are working from home, stores are struggling to stock their shelves and health officials are scrambling to respond to an unknown number of patients who will be taken ill with COVID-19.

Unprecedented actions taken since Wednesday to halt the spread of the coronavirus, from the total shutdown of K-12 school districts to significant curtailment of public gatherings, will surely have significant social and economic costs.

Especially hard hit will be those in the service industry who may not get paid in the near future or who must now try to find child care while they continue to fill essential jobs in health care, law enforcement, logistics and retail.


The question is, what does all of this swift action buy? How does it change the end game for the COVID-19 epidemic? How long will it take for the highly contagious virus to run its course? There are several factors at play.

Judging by the studies now coming out of China and other nations that have already taken such measures, infectious disease experts seem universally confident that having as many people stay as far away from each other as they can for several weeks in a row will make a significant difference.

But it’s tough, they add, to say how much novel coronavirus will still be circulating in the community come New Year’s Day, or even the Fourth of July, because we have not yet done enough testing to know with confidence how much is here already.

Dr. Robert “Chip” Schooley a UC San Diego infectious disease specialist and editor of the medical journal Clinical Infectious Diseases, noted that testing in the United States so far has been reserved mostly for those who have traveled to countries where COVID-19 outbreaks started months ago.


It will not be until significantly more people who have not traveled are tested that there will be a robust-enough measure of how broadly the disease has spread from person to person in communities, he said.

Dr. Robert “Chip” Schooley is an infectious disease specialist and senior director at UC San Diego School of Medicine. (UCSD)

“We need to be in a situation where we have a larger number of people being tested for a wider variety of symptoms and that will begin to fill in the blanks about how much virus is actually circulating,” Schooley said.

But that’s not to say, he added, that the data we do have indicates that the actions taken in America were an overreaction.


“Every day we see more and more of these dots that are lining up to make it clear that this virus is actually pretty widespread, and we really do need to be taking these actions,” Schooley said. “These are not carelessly thought out things that are being done just because we can do them. They’re being done because we need to do them.”

In the past seven days, the phrase “flatten the curve” moved from discussions among a select group of forward-thinking epidemiologists to the common lexicon, popping up on social media as results from ongoing studies in other places began to show the power of broad, unified action designed to prevent people from passing infections to each other.

Graphs showing the slow-growing number of cases over time in Singapore and South Korea, and a reversal of the out-of-control pattern in China, arrived just as America’s numbers spiked, reaching 1,280 by Wednesday and 2,174 by Saturday, according to Johns Hopkins University.

Many quickly learned that the commonality among these nations has been significant social distancing campaigns that are able to break chains of transmission by ruthlessly canceling public events, keeping kids home from school and being relentless about spotting new cases early and isolating the infected quickly, even if it means keeping them separate from their families.


While the pace and longevity of the epidemic is an open question, everyone already knows that reaching a state of herd immunity in communities across the nation will bring its true end. Herd immunity is a hard-earned state in which a large enough percentage of a population has already established immunity to a disease that it’s difficult to sustain long chains of person-to-person transmissions. When many of the people an infected person encounters are already immune, outbreaks tend to stay small.

Specific pathogens require different thresholds of community immunity to harness the power of the herd, and those thresholds are based on just how infectious a virus or bacteria is. Measles, for example, requires between 93 percent to 95 percent because it’s highly infectious, with each case causing between 12 and 18 additional cases, according to a 2017 study from the London School of Hygiene and Tropical Medicine.

It’s probably not that high for novel coronavirus, said mathematical epidemiologist Gerardo Chowell, chair of the Department of Population Health Sciences at Georgia State University in Atlanta.

Though no formal estimate has yet been adopted, Chowell, who is part of a team that has been modeling the movement of this new virus through populations in China and several other countries, said he would guess it’s higher than the 50 percent threshold for SARS, which is caused by a different coronavirus.


“The optimal threshold, I would think, based on what we’ve seen so far, should be between 60 percent and 70 percent for herd immunity,” Chowell said.

Communities can get there one of two ways: either lots of people get sick and recover, or a vaccine is developed that can confer immunity to people without them having to get sick. So far, experts say a vaccine is at least one year away, so it’s down to getting sick and recovering at the moment.

Only scientists developing vaccines are chasing the herd at the moment. The idea behind the current strategy of social distancing is to spread out the illness over a long enough period of time that those who do end up with life-threatening illnesses don’t get sick all at once and overwhelm local treatment capacity.

Chowell agreed that there is just not enough testing data in the U.S. yet to say with confidence just how widespread novel coronavirus already is. So, until data collection catches up with the epidemic, it’s difficult to start making predictions about the end game.


But that doesn’t mean that there is no way to know what the effect of significant social distancing measures, combined with aggressive public health investigation work to quickly identify and isolate those who are infected, will be.

Gerardo Chowell is a professor of mathematical epidemiology at Georgia State University. (Georgia State University)

On Feb. 14, scientists from Georgia State, Tulane University in New Orleans and the Infectious Disease Prevention and Control Branch in Ottawa, jointly released a paper in the journal Infectious Disease Modeling that made an ambitious prediction. Based on observations of case rates in China reported from Feb. 5 through Feb. 9, the research team said that the epidemic in China had “reached a saturation point” due largely to “the wide spectrum of social distancing measures implemented by the Chinese government.”

Though there was another big jump in numbers just at the paper came out, China’s new case rate subsequently stabilized, reaching 80,000 cases by mid-March and adding less than 1,000 more over the past two weeks, according to the Johns Hopkins Coronavirus Resource Center counts.


On Wednesday, speaking hours before President Donald Trump announced a travel ban to Europe and the NBA postponed the remainder if its season, Chowell predicted, based on the modeling he has done of China, Singapore and other countries, that the pace of the novel coronavirus epidemic in the U.S. would be persistent but likely not as dramatic as it was in China.

“My best guess is it will be a smoldering outbreak in the U.S. for roughly a year and, hopefully, by then we will have a vaccine,” Chowell said on Wednesday.

The breadth and scope of the social distancing recommendations put in place just a few days ago, Chowell said, do change the game. But not likely the smoldering nature of the epidemic. Social distancing will work better in some places than others, and some places, like Washington State, are already far ahead of others in terms of community spread.

“Some cities are already being hit much harder than others, but, in the long run, thinking about the next 12 months or so, given the public health measures and social distancing measures that are being put in place now, I do think we should be getting toward something that looks more like the growth rate that we see Singapore or Hong Kong models,” Chowell said.


Ben Lopman is an infectious disease epidemiologist at Emory University. (Emory University)

Benjamin Lopman, professor of epidemiology at Rollins School of Public Health, Emory University, also in Atlanta, agreed that social distancing is likely to have a real impact. Such precautions helped end the 1918 flu pandemic, and cities such as St. Louis that canceled events early in the epidemic did fare better than those such as Philadelphia that stuck with their social schedules.

“What we can learn from history is that cities that were very aggressive in their kind of social distancing activities, like canceling mass gatherings such as parades, were much more effective at getting that curve to flatten out,” Lopman said.

While looking at how this novel coronavirus moved through populations is instructive, it’s important to remember that countries are not carbon copies of each other, Lopman added.


“This is the same virus in every country, but it’s going into different populations,” Lopman said. “The structure of each population, and how people mix socially with each other, is different in different places. So while we can draw some lessons from what has occurred in other places, we shouldn’t expect it to be exactly the same here.”

Many in the public, who have seen their immediate social calendars evaporate, might be wondering about the events that are still far enough away that they haven’t yet been canceled. The San Diego County Fair, for example, is still scheduled to run from June 5 to July 5, and San Diego’s Comic-Con International, which perennially brings more than 130,000 visitors from all over the world to the San Diego Convention Center, is still on the books from July 23 through July 26.

Will the social distancing mandates now in effect be enough to save these beloved summer celebrations? It’s hard to know, because organizers for both events declined to identify the final dates by which they must make go/no go decisions. For the moment, though, a public health directive issued Thursday caps the size of gatherings at no more than 250 people. Public health officials have said that they will revisit their decision on gathering limits regularly, looking at the actual rate of coronavirus detection in the community to determine whether the caps are still necessary.

Though all three experts said they would like to get a look at additional data in the next few weeks before making any firm predictions about how quickly individual communities might be able to return to normal activity levels, they had slightly different gut feelings about where things are headed.


Lopman was the most skeptical: “I think it’s wishful thinking that this will be gone by the summer.”

Chowell was the most optimistic: “I think that you would need about five or six weeks, and by the end of May, if not earlier, you should be in a position to decide whether or not Comic-Con should take place, and that, by the way, also applies to the Olympics.”

Schooley leaned skeptical as well: “I would personally think right now that it’s unlikely that they will occur. Some might, but it depends on how successful we are in shutting things down now.”

Events are visible mileposts for what’s being missed, but Schooley said everyone would do well to remember what’s invisible. That’s the unknown and unknowable number of vulnerable people whose lives will end up being saved because they they don’t get infected in the first place.


“By doing what we’re doing, we’re saving people’s lives as we speak, and it’s really important for people to understand that,” Schooley said.