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R0, the Messy Metric That May Soon Shape Our Lives, Explained R0, the Messy Metric That May Soon Shape Our Lives, Explained
(1 day later)
World leaders and public health experts are poised to spend the coming months or years obsessed with a variable known as R0.World leaders and public health experts are poised to spend the coming months or years obsessed with a variable known as R0.
Pronounced “R-naught,” it represents the number of new infections estimated to stem from a single case.Pronounced “R-naught,” it represents the number of new infections estimated to stem from a single case.
In other words, if R0 is 2.5, then one person with the disease is expected to infect, on average, 2.5 others.In other words, if R0 is 2.5, then one person with the disease is expected to infect, on average, 2.5 others.
An R0 below 1 suggests that the number of cases is shrinking, possibly allowing societies to open back up. An R0 above 1 indicates that the number of cases is growing, perhaps necessitating renewed lockdowns or other measures.An R0 below 1 suggests that the number of cases is shrinking, possibly allowing societies to open back up. An R0 above 1 indicates that the number of cases is growing, perhaps necessitating renewed lockdowns or other measures.
But R0 is messier than it might look. It is built on hard science, forensic investigation, complex mathematical models — and often a good deal of guesswork. It can vary radically from place to place and day to day, pushed up or down by local conditions and human behavior.But R0 is messier than it might look. It is built on hard science, forensic investigation, complex mathematical models — and often a good deal of guesswork. It can vary radically from place to place and day to day, pushed up or down by local conditions and human behavior.
Yet for all its vagaries, R0 is expected to shape our world in the coming months and possibly years as governments and health experts treat it as the closest thing to a compass in navigating the pandemic.Yet for all its vagaries, R0 is expected to shape our world in the coming months and possibly years as governments and health experts treat it as the closest thing to a compass in navigating the pandemic.
What follows is a simple guide to how this metric works, why it matters and how to think about it.What follows is a simple guide to how this metric works, why it matters and how to think about it.
The term is borrowed from the study of demographics, where it is used to describe birthrates.The term is borrowed from the study of demographics, where it is used to describe birthrates.
R refers to reproduction and 0 to the zeroth generation, as in patient zero. Together, they are typically called the basic reproduction number.R refers to reproduction and 0 to the zeroth generation, as in patient zero. Together, they are typically called the basic reproduction number.
It is calculated from innate features of a disease, like how easily it jumps from one person to the next, along with elements of human behavior that shape how often sick and susceptible people will come into contact.It is calculated from innate features of a disease, like how easily it jumps from one person to the next, along with elements of human behavior that shape how often sick and susceptible people will come into contact.
The resulting number is meant to help model an outbreak’s possible trajectory.The resulting number is meant to help model an outbreak’s possible trajectory.
Say that 1,000 people have a seasonal flu whose R0 is estimated at 1.3.Say that 1,000 people have a seasonal flu whose R0 is estimated at 1.3.
They would be expected to infect 1,300 people. That second generation would go on to infect another 1,690.They would be expected to infect 1,300 people. That second generation would go on to infect another 1,690.
That can add up. By the 10th generation, about 30 days time, 42,621 people would have caught the flu.That can add up. By the 10th generation, about 30 days time, 42,621 people would have caught the flu.
But any R0 is just an estimate and, epidemiologists stress, an imperfect one.But any R0 is just an estimate and, epidemiologists stress, an imperfect one.
A paper published last year in Emerging Infectious Diseases, an academic journal, described the metric as important but warned that it can be “easily misrepresented, misinterpreted and misapplied.”A paper published last year in Emerging Infectious Diseases, an academic journal, described the metric as important but warned that it can be “easily misrepresented, misinterpreted and misapplied.”
There is no consensus for how to measure it. Much of the underlying math relies, by necessity, on educated guesses and on human factors that can change unpredictably.There is no consensus for how to measure it. Much of the underlying math relies, by necessity, on educated guesses and on human factors that can change unpredictably.
For this reason, most diseases are given a range, rather than a single figure. SARS is usually described as having an R0 of 2 to 5 — an enormous difference.For this reason, most diseases are given a range, rather than a single figure. SARS is usually described as having an R0 of 2 to 5 — an enormous difference.
Tellingly, scientists are still disputing and revising estimates for diseases that have been studied for years; R0 figures for measles have ranged from 3.7 to 203.Tellingly, scientists are still disputing and revising estimates for diseases that have been studied for years; R0 figures for measles have ranged from 3.7 to 203.
Still, for all its flaws, it’s useful shorthand for both experts studying the disease and leaders trying to manage it.Still, for all its flaws, it’s useful shorthand for both experts studying the disease and leaders trying to manage it.
In practice, there is no such thing as a fixed R0. It’s better to think of this number as a starting point for the virus’s behavior in the absence of real-world human or environmental factors.In practice, there is no such thing as a fixed R0. It’s better to think of this number as a starting point for the virus’s behavior in the absence of real-world human or environmental factors.
New figures are coming out all the time. But, generally, studies now estimate that the pathogen that causes Covid-19 has an R0 of 2 to 2.5.New figures are coming out all the time. But, generally, studies now estimate that the pathogen that causes Covid-19 has an R0 of 2 to 2.5.
That’s significantly higher than the flu and within lower-end ranges for SARS, another coronavirus.That’s significantly higher than the flu and within lower-end ranges for SARS, another coronavirus.
To know how quickly a virus spreads, you also need its serial interval, or average time between each successive infection. Some studies estimate the coronavirus’s at 4 to 4.5 days. That’s almost twice as fast as SARS, which is why the coronavirus spreads so much more quickly.To know how quickly a virus spreads, you also need its serial interval, or average time between each successive infection. Some studies estimate the coronavirus’s at 4 to 4.5 days. That’s almost twice as fast as SARS, which is why the coronavirus spreads so much more quickly.
The serial interval, though, is considered more or less fixed. People can heavily influence R0, which is why it receives so much more attention than other metrics.The serial interval, though, is considered more or less fixed. People can heavily influence R0, which is why it receives so much more attention than other metrics.
The term can also be used to describe a snapshot in time: an estimate of how the virus is reproducing on the ground in a given time and place.The term can also be used to describe a snapshot in time: an estimate of how the virus is reproducing on the ground in a given time and place.
For example, during China’s initial outbreak, one study estimated, the virus spread with an R0 of 5.7 — a catastrophically high figure.For example, during China’s initial outbreak, one study estimated, the virus spread with an R0 of 5.7 — a catastrophically high figure.
Governments increasingly use R0 as a metric for whether their country’s cases are growing faster than they can manage or shrinking as quickly as they’d like.Governments increasingly use R0 as a metric for whether their country’s cases are growing faster than they can manage or shrinking as quickly as they’d like.
Interest in R0 has grown so intense that a video of Angela Merkel, the restrained German chancellor rarely associated with viral videos, explaining the variable has been viewed nearly nine million times.Interest in R0 has grown so intense that a video of Angela Merkel, the restrained German chancellor rarely associated with viral videos, explaining the variable has been viewed nearly nine million times.
“We are now at about a reproduction factor of 1, so one person is infecting another one,” Ms. Merkel said at a press event last week. “If we get to the point where everybody infects 1.1 people, then by October we will reach the capacity of our health care system.”“We are now at about a reproduction factor of 1, so one person is infecting another one,” Ms. Merkel said at a press event last week. “If we get to the point where everybody infects 1.1 people, then by October we will reach the capacity of our health care system.”
When a country has more patients than intensive care beds, death rates can spike drastically.When a country has more patients than intensive care beds, death rates can spike drastically.
At an R0 of 1.2, Ms. Merkel went on, Germany would cross that threshold in July. At an R0 of 1.3, it would happen in June.At an R0 of 1.2, Ms. Merkel went on, Germany would cross that threshold in July. At an R0 of 1.3, it would happen in June.
“So that’s where you see how small the margin is,” she said.“So that’s where you see how small the margin is,” she said.
But real-time R0 estimates like Germany’s are, however sophisticated, highly speculative. It is an estimate built on other estimates, some more informed than others.But real-time R0 estimates like Germany’s are, however sophisticated, highly speculative. It is an estimate built on other estimates, some more informed than others.
Still, it is one of our only metrics for guessing at how well lockdowns and other policies are working — and therefore for determining whether and when those policies are worth their enormous economic and social costs.Still, it is one of our only metrics for guessing at how well lockdowns and other policies are working — and therefore for determining whether and when those policies are worth their enormous economic and social costs.
No. It means, assuming the numbers are correct, that the virus’s spread has been paused.No. It means, assuming the numbers are correct, that the virus’s spread has been paused.
Where R0 drops below 1, this means that every, say, 100 sick people will infect fewer than 100 others. Each successive generation of infections will be smaller than the last.Where R0 drops below 1, this means that every, say, 100 sick people will infect fewer than 100 others. Each successive generation of infections will be smaller than the last.
Updated June 30, 2020
Common symptoms include fever, a dry cough, fatigue and difficulty breathing or shortness of breath. Some of these symptoms overlap with those of the flu, making detection difficult, but runny noses and stuffy sinuses are less common. The C.D.C. has also added chills, muscle pain, sore throat, headache and a new loss of the sense of taste or smell as symptoms to look out for. Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.
Scientists around the country have tried to identify everyday materials that do a good job of filtering microscopic particles. In recent tests, HEPA furnace filters scored high, as did vacuum cleaner bags, fabric similar to flannel pajamas and those of 600-count pillowcases. Other materials tested included layered coffee filters and scarves and bandannas. These scored lower, but still captured a small percentage of particles.
A commentary published this month on the website of the British Journal of Sports Medicine points out that covering your face during exercise “comes with issues of potential breathing restriction and discomfort” and requires “balancing benefits versus possible adverse events.” Masks do alter exercise, says Cedric X. Bryant, the president and chief science officer of the American Council on Exercise, a nonprofit organization that funds exercise research and certifies fitness professionals. “In my personal experience,” he says, “heart rates are higher at the same relative intensity when you wear a mask.” Some people also could experience lightheadedness during familiar workouts while masked, says Len Kravitz, a professor of exercise science at the University of New Mexico.
The steroid, dexamethasone, is the first treatment shown to reduce mortality in severely ill patients, according to scientists in Britain. The drug appears to reduce inflammation caused by the immune system, protecting the tissues. In the study, dexamethasone reduced deaths of patients on ventilators by one-third, and deaths of patients on oxygen by one-fifth.
The coronavirus emergency relief package gives many American workers paid leave if they need to take time off because of the virus. It gives qualified workers two weeks of paid sick leave if they are ill, quarantined or seeking diagnosis or preventive care for coronavirus, or if they are caring for sick family members. It gives 12 weeks of paid leave to people caring for children whose schools are closed or whose child care provider is unavailable because of the coronavirus. It is the first time the United States has had widespread federally mandated paid leave, and includes people who don’t typically get such benefits, like part-time and gig economy workers. But the measure excludes at least half of private-sector workers, including those at the country’s largest employers, and gives small employers significant leeway to deny leave.
So far, the evidence seems to show it does. A widely cited paper published in April suggests that people are most infectious about two days before the onset of coronavirus symptoms and estimated that 44 percent of new infections were a result of transmission from people who were not yet showing symptoms. Recently, a top expert at the World Health Organization stated that transmission of the coronavirus by people who did not have symptoms was “very rare,” but she later walked back that statement.
Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.
A study by European scientists is the first to document a strong statistical link between genetic variations and Covid-19, the illness caused by the coronavirus. Having Type A blood was linked to a 50 percent increase in the likelihood that a patient would need to get oxygen or to go on a ventilator, according to the new study.
The unemployment rate fell to 13.3 percent in May, the Labor Department said on June 5, an unexpected improvement in the nation’s job market as hiring rebounded faster than economists expected. Economists had forecast the unemployment rate to increase to as much as 20 percent, after it hit 14.7 percent in April, which was the highest since the government began keeping official statistics after World War II. But the unemployment rate dipped instead, with employers adding 2.5 million jobs, after more than 20 million jobs were lost in April.
If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)
If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.
But people can still get sick, and people can still die. It can take a long time for countries to see the virus fully recede, especially if the initial outbreak was bad.But people can still get sick, and people can still die. It can take a long time for countries to see the virus fully recede, especially if the initial outbreak was bad.
Italy, for example, recently estimated that its social and economic restrictions had pushed the virus’s R0 down to 0.8 — a huge achievement won at a heavy cost.Italy, for example, recently estimated that its social and economic restrictions had pushed the virus’s R0 down to 0.8 — a huge achievement won at a heavy cost.
How long might it take Italy to resemble South Korea, which is tentatively reopening as it confirms about 10 new cases per day?How long might it take Italy to resemble South Korea, which is tentatively reopening as it confirms about 10 new cases per day?
Italy reported 15,918 new cases in the past five days, a workable shorthand for the number of people who might still be infectious. At an R0 of 0.8, it would take 26.8 generations of the virus for Italy’s new infections to pace South Korea’s.Italy reported 15,918 new cases in the past five days, a workable shorthand for the number of people who might still be infectious. At an R0 of 0.8, it would take 26.8 generations of the virus for Italy’s new infections to pace South Korea’s.
At four days per generation, that’s about 100 days, or early August. And that’s only if the status quo — lockdown — is maintained.At four days per generation, that’s about 100 days, or early August. And that’s only if the status quo — lockdown — is maintained.
Three and a half more months of social restrictions would be costly for Italy’s already-strained society and economy. And it would not be a guarantee. Even South Korea has measures in place to reimpose lockdowns if cases resurge.Three and a half more months of social restrictions would be costly for Italy’s already-strained society and economy. And it would not be a guarantee. Even South Korea has measures in place to reimpose lockdowns if cases resurge.
This is why some experts believe that, in the coming months or years, government measures will not be aimed at simply driving down R0 as low as possible, but at managing it within acceptable levels.This is why some experts believe that, in the coming months or years, government measures will not be aimed at simply driving down R0 as low as possible, but at managing it within acceptable levels.
In such a scheme, social and economic restrictions would be lifted and reimposed in response to fluctuations in the R0. But no one knows what the right balance would be, much less how to achieve it.In such a scheme, social and economic restrictions would be lifted and reimposed in response to fluctuations in the R0. But no one knows what the right balance would be, much less how to achieve it.
A Harvard University study estimated that keeping new cases within what the health care system can manage could require calibrating off-and-on lockdowns through mid-2022.A Harvard University study estimated that keeping new cases within what the health care system can manage could require calibrating off-and-on lockdowns through mid-2022.
Official efforts to track R0 are spotty but growing more common.Official efforts to track R0 are spotty but growing more common.
Several European countries now report estimates below 1, but levels of success remain uncertain.Several European countries now report estimates below 1, but levels of success remain uncertain.
Germany puts its own at 0.9, up from a recent low of 0.7, which had led Ms. Merkel to ease restrictions. Governments face gut-wrenching dilemmas over whether to accept such upticks as necessary evils.Germany puts its own at 0.9, up from a recent low of 0.7, which had led Ms. Merkel to ease restrictions. Governments face gut-wrenching dilemmas over whether to accept such upticks as necessary evils.
One study from France estimated that timely lockdowns pushed R0 down to 0.5 from 3.3, a stunning transformation.One study from France estimated that timely lockdowns pushed R0 down to 0.5 from 3.3, a stunning transformation.
Still, French cases jumped the day after the study was published, in part because nursing home infections had not previously been recorded, a reminder that R0 estimates are imperfect shorthand.Still, French cases jumped the day after the study was published, in part because nursing home infections had not previously been recorded, a reminder that R0 estimates are imperfect shorthand.
India, whose enormous population and rickety health care system make it one of the pandemic’s most-watched countries, estimates its R0 to have declined to 1.36 from 1.55. That’s low, but still above 1 — meaning case numbers are growing.India, whose enormous population and rickety health care system make it one of the pandemic’s most-watched countries, estimates its R0 to have declined to 1.36 from 1.55. That’s low, but still above 1 — meaning case numbers are growing.
It is difficult to assign the United States a single R0 figure. The country has multiple concurrent outbreaks, each with its own dynamics and each at a different point in its life cycle.It is difficult to assign the United States a single R0 figure. The country has multiple concurrent outbreaks, each with its own dynamics and each at a different point in its life cycle.
The former founders of Instagram set up a website that estimates state-by-state Rt values, a variation on R0 that accounts for rates of transmission. Though it is not associated with professional epidemiologists or public health experts, it has received heavy attention, reflecting the hunger for information on this useful but fuzzy metric.The former founders of Instagram set up a website that estimates state-by-state Rt values, a variation on R0 that accounts for rates of transmission. Though it is not associated with professional epidemiologists or public health experts, it has received heavy attention, reflecting the hunger for information on this useful but fuzzy metric.