Unlike seasonal influenza or common colds, where the transmission chains

9 min readDec 3, 2020

WWhile the worst Covid-19 outbreaks in the United States so far have occurred in a relative handful of large cities and other locales, experts say the steep rise in cases — the curve — will come to communities large and small across the country in coming days and weeks. Already some rural counties are seeing outbreaks.

For just about everyone else, it’s a matter of time.
And this may be just the first wave of a pandemic that could return in multiple seasons, all depending on whether it can be contained by physical distancing, a potential vaccine, or other preventive measures.
“This is an extraordinarily transmissible virus, and I think it’s more transmissible than we recognize,” says Michael Mina, assistant professor of epidemiology at Harvard T.H. Chan School of Public Health.
Mina has “little faith” in the accuracy or extent of Covid-19 testing so far. Between people who are sick but have not been tested and the unknown number of people carrying the disease without any symptoms and transmitting it, Mina and other epidemiologists says it’s completely unknown how many people are actually infected.
“We really don’t know if we’ve been 10 times off or 100 times off in terms of the cases,” Mina says. “Personally, I lean more to 50 or 100 times off.”
That means instead of more than a million cases in the world right now, there could be anywhere from 10 million to perhaps 100 million. That also means the extreme preventive measures like stay-at-home orders could last months, not weeks, Jeremy Konyndyk, a senior policy fellow at the Center for Global Development, tells the health news site Stat.
Few doubt that the effects will be grave, no matter what the actual number of cases is right now.
Total U.S. deaths from Covid-19 are projected to climb steeply in coming weeks and reach 93,531 by August 4, according to the Institute for Health Metrics and Evaluation (IHME), an independent global health research center at the University of Washington. The estimate, which includes a wide range of uncertainty, was cited by Dr. Deborah Birx, the White House coronavirus response coordinator.
‘It’s all coming soon’
“The spread and scope of Covid-19 is just immense, and that’s because it’s been spreading unchecked, and still is,” says Mark Cameron, PhD, an immunologist and medical researcher in the School of Medicine at Case Western Reserve University in Ohio.
During the 2003 SARS epidemic, which was also caused by a coronavirus, Cameron worked at Toronto General Hospital, the only major city that experienced an outbreak outside of China. That disease and this one yielded similar data on many measures except one: the ratio of severe to mild cases. “People who got SARS in 2003 got very sick very fast, so it was easy to identify them and isolate and treat them,” Cameron says. Conversely, a far lower percentage of people had mild or no symptoms with SARS, so it did not spread as rapidly as Covid-19.
Many of the same extreme preventive measures were taken in Toronto as are being done now in states across America, Cameron says, and the 2003 epidemic was contained, and the virus was apparently eliminated from the human population.
“This virus is very smart, and it spreads very easily,” Cameron says of Covid-19. “This is unprecedented. This is a 100-year pandemic.”
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The first U.S. case of Covid-19 was reported on January 21, 2020. This chart shows the number of new cases each day since then, through April 7. Credit: Johns Hopkins University School of Medicine
New York’s coronavirus outbreak illustrates how population density fosters more rapid spread of a disease, Cameron and other experts say. But every city and state that has yet to see severe outbreaks of Covid-19 will get its turn, Cameron tells me. The curves will be similar, even if the total numbers of cases and deaths are lower.
“Every state will experience their own curve and their own peak,” he says.
Mina agrees, adding another twist that has yet to play out: It’s known that people with underlying health conditions are at greater risk for severe symptoms and death from the coronavirus. Areas with a high proportion of people who have heart disease and diabetes may therefore experience more severe death ratios than what’s been seen so far. Mina cited Memphis, New Orleans, and Atlanta as three examples.
“These are places that I think have the potential to be hit very hard,” Mina says. “It’s all coming soon.”
Making matters potentially worse, unlike New York and other major cities that have large, highly capable hospitals, many rural communities have none. St. John the Baptist Parish in Louisiana, near Baton Rouge, has the highest per capita coronavirus mortality rate in the nation right now and exactly zero hospitals, according to Politico.
How the curves ultimately play out depends largely on the extent to which preventive measures are put in place, kept in place, and followed by the public.
“Our estimated trajectory of Covid-19 deaths assumes continued and uninterrupted vigilance by the general public, hospital and health workers, and government agencies,” says Dr. Christopher Murray, director of IHME, the organization publishing the death projections cited by the White House. “The trajectory of the pandemic will change — and dramatically for the worse — if people ease up on social distancing or relax with other precautions. We encourage everyone to adhere to those precautions to help save lives.”
“Unlike seasonal influenza, where the transmission chains get easier to break in the warm summer months, we cannot count on Covid-19 relenting simply because of a change of season.”
Time to prepare
Meanwhile, cities, counties, and states fortunate enough to have watched the havoc unfold elsewhere have had an opportunity to take strong spread-prevention actions while simultaneously making preparations akin to a war footing while case counts are relatively low.
One example of a state in waiting is Ohio, where Governor Mike DeWine issued a strong stay-at-home order on March 23. “We haven’t faced an enemy like we are facing today in 102 years — we are at war,” DeWine said.
That strict order and other physical distancing measures help explain why Ohio has about one-fourth as many cases as neighboring Michigan, says Dr. Robert Salata, a professor of medicine in epidemiology and international health at Ohio’s Case Western Reserve University.
Salata leads the medical response in an 18-institution united command center, similar to what the military uses in a time of war. “And this is a time of war,” he says in a phone interview. Cases are starting to spike, and Ohio is in week one of a four-week ramp-up to an expected peak, he says.
“It’s not totally chaotic or a real crisis at this point,” Salata says. “But it can become so, and we’re preparing for that inevitability.”
He and colleagues are taking a variety of measures:
Eliminating elective surgeries and cutting back on even semi-urgent care to reduce occupancy in the system to just 60% — much lower than normal.
Working with a local biodefense company to figure out how to resterilize and reuse protective gear.
Figuring out when infected hospital workers can return to work by testing 10 days after symptom onset and again 24 hours later and letting them return if they test negative but still have a cough. (But, of course, they wear a mask.)
Using this low-volume window of opportunity to study the Covid-19 cases they do have, including through clinical drug trials.
“Ohio has had more time to watch what’s been happening in Seattle and the Bay Area and New York to be proactive instead of reactive,” Cameron says. “But at the same time, what I’m seeing in the case data, in general every city or county is experiencing the same type of curve. Ohio might have been a little lucky so far, and population density and measures that were taken proactively will help us, but we can’t be complacent in terms of this spread and the case rates of infection that have been seen everywhere else.”
72% of all counties probably already have an outbreak
Given the underreporting of total cases, disease modelers at the University of Texas at Austin used the available data to project the likelihood that any given county in the United States already has an outbreak, meaning sustained human transmission, whether they realize it or not.
“If a county has detected only one case of Covid-19, there is a 51% chance that there is already a growing outbreak underway,” the researchers state. “Covid-19 is likely spreading in 72% of all counties in the U.S., containing 94% of the national population.”
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Probability of ongoing Covid-19 outbreaks for the 3,142 counties in the United States. The chance of an unseen outbreak in a county without any reported cases is 9%. A single reported case suggests that community transmission is likely. Source: Emily Javan, Dr. Spencer J. Fox, Dr. Lauren Ancel Meyers
“Proactive social distancing, even before two cases are confirmed, is prudent,” conclude researchers Emily Javan, Dr. Spencer Fox, and Dr. Lauren Ancel Meyers. “Although not entirely surprising, these risk estimates provide evidence for policymakers who are still weighing if, when, and how aggressively to enact social distancing measures.”
Second wave… and then more
Meanwhile, worst-case scenarios are not inevitable, says Dr. Harvey Fineberg, president of the Gordon and Betty Moore Foundation, a philanthropic organization, and former president of the U.S. National Academy of Medicine.
“That choice begins with a forceful, focused campaign to eradicate Covid-19 in the United States. The aim is not to flatten the curve; the goal is to crush the curve,” Fineberg writes in an April 1 editorial in the New England Journal of Medicine. “China did this in Wuhan. We can do it across this country in 10 weeks.” But that would require quickly taking a far more aggressive approach than the current U.S. response, six big steps, including:
Establishing a unified command at the federal level and for each state.
Solving the shortage of protective gear for health care workers.
Making available millions of diagnostic tests.
While what is done now is vital, decisions in the coming weeks and months could prove similarly weighty.
“We know from the SARS 2003 outbreak in Toronto that there is a well-documented wave of second infections caused by letting some of the close-contact and personal protective equipment (PPE) precautions be relaxed because they felt they were on the other side of the curve,” Cameron says. “Turns out they weren’t, and a new curve, a new outbreak, a second wave, occurred in Toronto. We need to avoid that.”
Already some Asian countries that had flattened their curves are seeing resurgences in new cases, including Singapore and Taiwan, according to the New York Times.
Next season and beyond
Further ahead looms another great unknown: whether Covid-19 will subside with warmer temperatures, as is typical of some coronaviruses and influenza.
Don’t bank on it.
“Unlike seasonal influenza or common colds, where the transmission chains get easier to break in the warm, humid, summer months, especially amongst communities with herd immunity, we cannot count on Covid-19 relenting simply because of a change of season,” Cameron says. “Covid-19 has already bulldozed through multiple different climates in the Northern and Southern hemispheres quite easily.”
Among South American countries as of April 4, Brazil had 7,910 diagnosed cases and 299 deaths, Chile had 3,737 cases and 22 deaths, and Ecuador had 3,163 cases and 120 deaths.
Even if the pandemic does lessen or go away this summer in the United States, that won’t mean it’s gone.
“It is more likely that Covid-19 will spread relatively unchecked by seasons until the surges and curves have run their course… in populations worldwide, then return seasonally, hopefully put in some check by those amongst us with preexisting immunity by having had it already,” Cameron says. A vaccine would also help, of course, but that’s thought to be months away.
Breaking the chain of transmission
Cameron cites the 2009 H1N1 “swine flu” pandemic as an example of how viruses can flout the seasonality rule. “It took firm hold in the spring and summer months of 2009 in Mexico and the U.S., spreading virtually worldwide from there until August 2010.”
The influenza pandemic of 1918–19 cycled through multiple seasons across two years, ultimately killing some 675,000 people in the United States and more than 50 million around the globe. (In Boston, a second wave hit during the first season when World War I ended and large crowds gathered to celebrate.)
If there is a notable dip in Covid-19 cases this summer, all it takes to reemerge in the fall is for infected people, whether from south of the equator or from a fresh pocket in the Northern Hemisphere, to travel.
“There has to be a chain of human transmission to support the seasonality of a particular illness,” Cameron explains. “So, breaking that transmission is absolutely critical. If it finds enough of a foothold in enough places that we don’t detect, it will reemerge in the fall.”

Unlike seasonal influenza or common colds, where the transmission chains

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