Despite the urgent demands on their time in this volatile situation, we’ve managed to score email interviews with three academic epidemiologists, getting the inside scoop from experts on how to interpret ongoing coronavirus news and know what’s really going on.
We spoke with:
- Dr. Neil Ferguson of Imperial College in London and the WHO Collaborating Centre for Infectious Disease Modeling, one of the authors of the WHO stochastic modeling study we discussed before
- Dr. Julien Riou of the University of Bern in Switzerland, one of the authors of the stochastic modeling study from Switzerland, which we also discussed
- Dr. He Daihai of Hong Kong Polytechnic University, one of the authors of a model fitting study similar to the Majumder study we previously covered
We spoke on a number of topics, including their inferences of the meaning behind current news, their near-term projections for what’s next with this outbreak, and most importantly, their expert judgment of which developments in the coming days and weeks will signal that the outbreak is becoming controlled — or that it could grow and worsen for a longer period of time.
How contagious is 2019-nCoV?
All three professors agreed that the ascertainment rate (the percentage of existing infections that doctors are actually identifying as 2019-CoV) has increased over time, and that the current rate of growth in confirmed cases (doubling every two days) is not all the result of actual viral contagion.
They expect the rate of growth in confirmed cases to drop as we get a more thorough grasp on who’s already infected, even if the virus is not controlled. Dr. Ferguson went so far as to suggest that the epidemic’s real doubling time could currently be about a week, while Dr. He estimated that reporting rate may have accounted for between one and three of the four doublings in case counts seen in the last eight days.
Dr. Riou stressed the uncertainty in current estimates. “This is because the ascertainment rate (the probability that a case is recognized and shows up in the counts) varies a lot from day to day. Estimations of total size based on the number of exported cases are more reliable. These are based on the number of sick people diagnosed in foreign countries compared to the total number of people that travelled. But even this approach doesn’t work anymore when people start to modify their behaviour according to the epidemic. After authorities start putting control measures at airports, and after the fear of contamination leads to people modifying their mobility according to the epidemic, these estimates aren’t adapted anymore.”
In comparing the Wuhan virus’s contagiousness to SARS, all three expressed uncertainty. Dr. He and Dr. Riou pointed to the changes in China’s urban landscape since 2003 which may have made it easier for the virus to spread, and to the uncertainty about both current case numbers and the size of the initial transmission from wild animals.
Dr. Ferguson suggested that while the reproduction number might be similar to SARS, it could be that 2019-nCoV might have more potential to spread in communities at large than SARS.
“I think control will be very difficult”
Dr. Ferguson and Dr. Riou both commented on the Chinese government’s aggressive campaign of quarantines and lockdowns:
“I think China is trying to do everything it can to get ahead of this epidemic now and control spread,” Dr. Ferguson said. “Reported confirmed cases are likely lower than estimated case numbers because hospitals and testing capacity is overwhelmed in Wuhan. Whether they succeed in control depends on how many mildly symptomatic cases there are which escape detection. I think control will be very difficult.”
Dr. Riou called the response “very aggressive,” and said that while “everyone is very impressed by the lockdown…it is difficult to say at this point if it will succeed.”
When will we be able to tell whether the epidemic is being controlled or not?
All three academics said that transmission of the coronavirus in countries outside China would be the most important indicator.
Dr. Ferguson suggested that more value would come from watching case numbers in wealthy and distant areas than those in Hubei. “At this point, growth in case numbers in wealthy provinces like Guangdong, plus evidence of spread in other countries, will be the best indicators of whether control is likely to succeed,” he said.
Dr. He said that with the high uncertainty around some key epidemiological parameters, the only thing which would convince him the epidemic was being controlled was “The slow-down of daily confirmed cases/mortality…and whether there is local spreading in other cities or regions.”
Dr. Riou said that it is still possible that the epidemic will be controlled, as SARS was, and that the more worrisome indication that it might remain uncontrolled would be “evidence of sustained transmission in the general population outside of China, [i.e.] two or three generations of human-to-human transmission outside of hospitals. This would indicate a true potential for an actual pandemic that will be really challenging to stop.”
How important is the news about asymptomatic transmission?
Stories of people transmitting the virus without first showing symptoms have recently come up in the news, so we were able to ask about that.
Dr. Ferguson sounded a skeptical note. “I remain to be convinced that asymptomatic transmission is substantial enough to be important,” he said. “I’d want to see more examples documented.”
Dr. Riou said that while he takes the Lancet report at face value and asymptomatic transmission cannot be ruled out, it was difficult to be certain about reports of asymptomatic transmission due to possible attribution errors in the chain of transmission. He was willing to entertain the possibility of an incubation period (the time between infection and first symptoms) as short as 3-6 days — a shorter incubation period makes asymptomatic transmission less likely, since peoples symptoms come on quicker.
Dr. Ferguson, in contrast, indicated his current view placed incubation periods in the 5-10 day range.
When will we know how deadly 2019-nCoV is compared to SARS?
All three professors agreed that there’s considerable uncertainty.
Dr. He cited recent a recent study from the University of Hong Kong on the first 41 confirmed cases, which had a 14% fatality rate among hospitalized cases, and a discussion suggesting that after adjustment for the low ascertainment rate, the overall case fatality rate might be as low as under 1%.
Dr. Riou said, “Fatality rates are typically overestimated early in an epidemic, because of the focus on the sickest individuals. Very sick individuals are more likely to be recognized and are also more likely to have fatal complications.”
Dr. Ferguson emphasized that in the long run, cohort studies beginning with patients just exhibiting their first symptoms would be the most reliable way to estimate CFRs, but said that such studies are “very difficult to run in an epidemic.”
Dr. Riou’s closing thoughts
Dr. Riou said the two most important things for everyone to keep an eye on were “whether sustained transmission in other countries exists [and] the possibility of asymptomatic transmission… because it has implication on control measures.”
Dr. Riou closed on a thoughtful note. “Later will come the time of evaluating strategies and finding out what really happened and how to better prevent it. Now we should focus on containing the spread.”
He continued: “It is important to accept that uncertainty is scary, but perfectly normal in this kind of hectic situation. We have to be clear about what we know and what we don’t know.”
“What we know is that this new coronavirus is very transmissible between humans, and that we need to do our best to limit this transmissibility by raising awareness and identifying risky situations. We cannot be sure for now how deadly this new virus is, but if the disease cannot be contained, even small fatality rates could mean many deaths in absolute value.”
As the epidemic has grown to encompass over 4,500 confirmed cases, with seven Chinese cities showing over 100 cases, and confirmed cases in 18 countries and territories outside China, and several days still remaining before we will see the effects of the quarantine, watching these key points will remain the best way to tell signal from noise.
