DER SPIEGEL: You predict that up to 60 percent of adults could become infected with the novel coronavirus. Isn’t that alarmist?
Lipsitch: I don't think so. It's of course a projection and, like any projection, it could be wrong. But if you have a reproductive number of an infectious disease of around two, which seems to be the estimates that we're getting right now (Eds: meaning that, on average, each infected person transmits the disease to two other people), then at a minimum, half the adult population needs to become infected before the spread can stop permanently. This is not an ungrounded estimation, but simply the basic math of epidemics.
DER SPIEGEL: Back in 2003, the World Health Organization warned that SARS could become a global epidemic. In the end, however, there were significantly fewer cases than the coronavirus has already caused as of today.
Lipsitch: Yes, but there was the risk that it could have become an epidemic. However, with SARS, almost all transmissions seem to have been in symptomatic patients, so you could control the spread more easily. That seems to be different with the virus that causes COVID-19. And our job as epidemiologists is to think about worst-case scenarios so we can spur the right actions to stop an epidemic.
DER SPIEGEL: If your prediction turns out to be true, how many people will die from the coronavirus?
Lipsitch: I don't want to speculate at this time. We think that around 1 or 2 percent of the symptomatic people died, but we don’t know how many people are really infected. It’s like an iceberg with the severe cases at the top level and the asymptomatic ones underneath the surface. We won't know how big the latter part of the iceberg is - and thus the true fatality rate – until the outbreak is over.
DER SPIEGEL: Can the virus still be contained?
Lipsitch: I don’t think the virus can be stopped anymore. It’s too late for that. In the United States, but also in Germany, we see transmission that isn't linked to anything known. So, the virus has already spread locally. That does seem to be a sign of things in some areas being out of hand.
DER SPIEGEL: Does tracing the contacts of infected people and placing them under self-quarantine at home still make sense?
Lipsitch: I think it does, in combination with other control measures. Even if we don’t trace all contacts, we can reduce the number of infections. What China has done collectively in their cities is effective. In the end, the total number of infected people may be similar but we slow the spread of the disease down significantly.
DER SPIEGEL: Why does this matter?
Lipsitch: First of all, it’s important because hospitals and doctors have a certain capacity and we don't want to exceed it. And secondly, with every week we are learning more about which drugs might work and we’ll certainly have better treatment protocols. If you had the choice, you would rather get the disease in six months from now than today.
DER SPIEGEL: Japan closed schools nationwide, Italy closed its universities. Is that a good public health measure?
Lipsitch: It's really hard to know. We have never dealt with an epidemic where the role of children was so unclear. Most infected kids don’t show symptoms, but we don’t know if they are still infectious. Closing schools countrywide even where there aren’t a lot of cases seems to be a measure that is hard to sustain. But in places where we saw community spread, it definitely makes sense.
DER SPIEGEL: You did extensive research on the influenza pandemic between 1918 and 1920, which killed more than 650,000 people in the United States alone. What did we learn from the flu pandemic?
Lipsitch: American cities reacted quite differently then. Philadelphia didn't respond until two weeks after the first influenza case when it closed schools and canceled public events. St. Louis, on the contrary, put in interventions early on, after two days. The peak death rate in Saint Louis was only one-eighth that of Philadelphia. The study showed that if cities intervened early and implemented aggressive social distancing, the epidemic slowed down and was less deadly in general.
The article you are reading originally appeared in German in issue 11/2020 (March 7th, 2020) of DER SPIEGEL.
DER SPIEGEL: How long have these drastic measures to be in place?
Lipsitch: We learned from the years 1918 to 1920 that lifting bans too early can cause the number of cases to increase again and you get a second peak. This is because the virus is, of course, still there. However, disruptive measures can’t be in place forever. So, it’s necessarily going to be a trade-off.
DER SPIEGEL: Will the novel coronavirus be among us for a long time?
Lipsitch: That's a strong possibility. However, there is some hope. There could be a long period with not much transmission in one or two years simply because it will be so widespread by then that most people have become immune to it.
Editor’s note: This interview was originally published in DER SPIEGEL on Friday, March 6, before the Italian government moved to place the entire country on lockdown.