After studying infectious diseases, epidemiologists like Helen Jenkins, of Boston University, and Bill Hanage, of Harvard, who are married, typically go one of two ways.
“They either become completely and utterly infection conscious,” Dr. Hanage said, “or they are the type of person who drops the toast and picks it up and wipes it off and eats it.”
“We would mostly be in the second category, but this has pushed us into the first category fairly visibly,” he continued, adding, “when the facts change, I update my priors” — a statistician’s term for what one believes and expects.
With the coronavirus pandemic, the facts update daily. To adapt, Dr. Hanage, who studies and teaches the evolution and epidemiology of infectious diseases, broadly embraced the guiding principle that he conveys to his students: “Come on, you’ve got to think like the pathogen! Try to see it from the point of view of the pathogens and their evolution. What is going to be most helpful to them? What is going to enable them to leave the most descendants?”
Recently, the family — Dr. Jenkins and Dr. Hanage, and their two daughters, ages 10 and 7 — gathered around their homemade whiteboard in the kitchen. Dr. Jenkins, whose work focuses on tuberculosis, which still kills about 4,000 people daily around the world, drew a simple tree diagram, as a way to clearly convey the value of cutting just one link in the coronavirus transmission chain.
The basic message: Very simple interventions, such as working from home and severing even one link, have an exponential effect. Every individual acting preemptively can make a huge difference.
“I started working from home a long time ago,” Dr. Hanage said.
“It was just a week ago,” Dr. Jenkins noted.
“Right, it was just a week ago,” he said.
“It feels like a year ago,” Dr. Jenkins said. “At the same time, we pulled our kids from school. And we spent the first part of last week urging parents in our local community to pull their kids from school, if they could. It was quite a difficult week.”
It was also a week of trying to keep up with work already planned, and of writing op-eds in The Guardian and The Washington Post on topics including testing issues in the United States, working from home and the controversial pandemic strategy in Britain. Their older daughter has daily Google Hangout meetings with her class and, with a friend, is creating a coronavirus PowerPoint information guide for their peers. There are whirlwind conference calls with colleagues, and live feeds with local and international radio and TV stations.
During one live interview this week, the couple’s 7-year-old daughter passed Dr. Hanage a note that read: “I’m lonely. I just just just hope it will be family day.” So far, family time focuses around Jenga play sessions, and dinner, followed by a nightly viewing of the 90s sitcom Frasier. “It makes us laugh, which is much needed,” Dr. Jenkins said — although she added that at the sight of anyone onscreen shaking hands, “I do find myself wincing.”
The following is an edited version of my phone and email conversations with Dr. Jenkins and Dr. Hanage, who were at their home in Cambridge, Mass.
Tell us about the tree diagram.
HJ: It simply shows what happens if you cut even one contact that would have resulted in transmission.
A tree diagram is not the type of thing epidemiologists would usually draw, because it seems obvious. But clearly we still need to do better at getting these concepts across to people.
BH: I build a lot of trees, but they are phylogenetic trees. My lab is very interested in figuring out ways of using genetics to detect transmission. The thing on our whiteboard is just a transmission tree. Every time you cut a link, you don’t just take out that link, you also take out all the potential cases and links descending from it. Those people could be infected by other means, later on, but every time each of us stops — or even just delays — an infection is a small victory.
Cutting a Link in the Chain of Transmission
A simple tree diagram shows how limiting contacts early might prevent many infections.
If each infected person spreads the coronavirus to two other people, the chain of infections would grow exponentially.
Avoiding even one social transmission early on in the chain could significantly reduce the number of infections.
Infection
avoided
If each infected person spreads the coronavirus to two other people, the chain of infections would grow exponentially.
Avoiding even one social transmission early on in the chain could significantly reduce the number of infections.
Infection
avoided
If each infected person spreads the coronavirus to two other people, the chain of infections would grow exponentially.
Avoiding even one social transmission early on in the chain could significantly reduce the number of infections.
Infection
avoided
If each infected person spreads the coronavirus to two other people, the chain of infections would grow exponentially.
Avoiding even one social transmission early on in the chain could significantly reduce the number of infections.
Infection
avoided
If each infected person spreads the coronavirus to two other people, the chain of infections would grow exponentially.
Avoiding even a single social connection early on in the chain could significantly reduce the number of infections.
Infection
avoided
HJ: I still feel really concerned about the complacency among so many people — people thinking that what happened in Wuhan, China, or Italy can’t possibly happen here. It’s really hard to see people in the U.K. and the U.S. not taking the problem seriously, and putting themselves and others at risk.
But individuals can do so much, too, because of the exponential increase of cases in an outbreak.
BH: It’s really instructive to compare what happened in Wuhan and what happened in Guangzhou. In Wuhan, they shut down when they had 495 cases in a city that is roughly the size of New York. In neighboring Guangzhou, by contrast, they took action when there were seven cases. The epidemic curve in Guangzhou was completely manageable. As we all know, in Wuhan it was absolutely …
HJ: Catastrophic.
BH: It led to the crisis in the hospitals. And this is the thing that is really important: The peak demand for critical care was roughly a month after the restrictions were put in place.
Right, so here we are, all doing some degree of extreme social distancing or sheltering at home. When will the peak hit? In a month?
BH: It could be a month from now, it could be longer. I want to be wary of getting into the weeds of complicated modeling or predictions. Instead, what I want to get across is: We know that this is a virus capable of doing what it did to Wuhan, and what it is now doing in Italy and Spain and what it will almost certainly do in the U.K. Washington State is coming under severe strain. Given what we know the virus is capable of, we should be preparing for it now.
HJ: We should have been preparing months ago.
And how long are the restrictions likely to last. When does it end? The report released Monday from modelers at Imperial College London suggested that we could be in for a long haul.
HJ: It’s a marathon, not a sprint. Everyone needs to come to terms psychologically with the idea that this is going to last a long time. It’s going to be a long-term effort to “flatten the curve.” If we can successfully bring down the case numbers to a manageable level, then we can reassess the situation. By then, we will hopefully have more science to inform our decision-making, and we will have ramped up testing capacity substantially.
We all must social-distance as much as possible to limit the impact. Utmost in my mind at the moment are the health care workers, some of whom are my friends, who are going to be on the front lines. They are the heroes, and by limiting transmission, we are all helping them do their jobs and save lives.
And the risks and interventions will change over time, as people better understand the situation. We should not think that this will blow over in a few weeks and then life will resume as it was before.
BH: Sustainability is a completely reasonable thing to be worried about. But it’s not an excuse for not taking urgent action now. We must not let the perfect be the enemy of the good.
The most sustainable measures will be put in place when the incidence of infection is low. Because when the incidence is high, the only way to save lives will be with really extreme interventions — the lockdowns, police on the streets like we have seen in Italy.
Coronavirus may not be dangerous to most people; if you are under 40 or so and have no comorbidities, you will probably be fine. But it is transmissible enough to infect a very large number of people. And even a small fraction of a very large number can be a large number — certainly enough to overwhelm our health care system.
It’s important to distinguish between the short term and the long term. The long term is hard to predict, but there are a lot of things we can do now, and many of them are common sense. As I keep saying: It’s epidemiology, not rocket science!
The uncertainty and unpredictability are confounding.
HJ: Yes, but an immediate crisis on our doorstep is that Personal Protective Equipment — masks, shields, gloves and so on, or P.P.E. — is running out for health care workers. We’d been hearing about a movement afoot to get the Defense Production Act invoked, and now that has happened, allowing mass production of P.P.E. and other necessary equipment. We are essentially entering a wartime situation and need to behave with that in mind; call your senators and other representatives, anything you can do to enact change. Health care workers are our front line soldiers, and we need to protect them. Talking of a “wartime situation” might sound scary, but remember: This is an opportunity for everyone to unite against a common enemy. I’ve been incredibly moved by how much important work everyone is doing to help one another. If we can harness that effectively, then I can start to feel more optimistic.
