The drug screens prompted by the SARS and MERS outbreaks have been useful for quickly identifying drug candidates.

But in terms of their epidemiology, “SARS and MERS were different from this coronavirus,” Allison McGeer explained at a Feb. 3 webinar by Evercore ISI.

McGeer is professor of laboratory medicine and pathobiology and of public health sciences at the University of Toronto, and was director of infection control at Mount Sinai Hospital during the 2002/2003 SARS pandemic. By her own description, she has “rather more experience with SARS than I would like.”

McGeer also has experience with both seasonal and pandemic influenza, and she described 2019-nCov as “somewhere between” other coronaviruses and influenza viruses in its transmission characteristics.

SARS and MERS patients (as well as Ebola patients) are most infectious after they have started showing symptoms, and did not easily spread via casual contact. As a result, the SARS pandemic, and the still-ongoing sporadic MERS outbreaks in the Kingdom of Saudi Arabia, are “very heavily focused in hospitals,” which enabled the eradication of the mutated SARS that was responsible for the second wave of infection in spring 2003, and makes containment of MERS outbreaks a relatively straightforward matter.

Allison McGeer, professor, University of Toronto

The 2019-nCoV virus is able to spread much more easily via human-to-human transmission. In both Germany and Japan, McGeer said, “transmission has been occurring without close contact.”

It is also likely that infected individuals are also contagious before they show symptoms. The first report of documented transmission from a symptom-free patient turned out to be in error. But many of those on the front-line – including National Institute of Allergy and Infectious Diseases Director Anthony Fauci – believe asymptomatic transmission is occurring.

To make matters even more challenging, symptoms start with fever and achiness rather than respiratory symptoms.

“We’re all still hoping that it is possible to control the transmission of this in the community,” McGeer said.

WHO officials expressed the same hope. At a press conference, Sylvie Briand, who is director of the WHO’s Infectious Hazards Management Department, told reporters that the agency believes that the virus can be prevented from becoming a pandemic, which is defined by uncontrolled spread in two countries.

But McGeer acknowledged that “there is an element of ‘I’m still hoping for this because the alternatives are not desirable’… whatever it is, it’s not good.”

For now, the WHO considers 2019-nCoV an epidemic with multiple locations.

Taken together, what’s known about the epidemiology of 2019-nCoV suggests that “this is a virus whose transmission we cannot successfully control, and that means that we’re going to have to live with it,” McGeer said. “And we don’t have enough data yet to know how bad living with it is going to be.”

How bad it is going to be depends on a combination of several unknown characteristics. In terms of infections, the key determinants are R0 (pronounced R-nought) and the case fatality rate.

So far, R0 appears to be between 1.5 and three for 2019-nCov, and the case fatality rate is around 2%, although that number is almost sure to change. In the short term, the case fatality rate will almost surely fall, as diagnostics are developed and deployed and milder cases are identified.

Electron micrograph of 1918 H1N1 influenza virus particles near a cell. Credit: NIAID

A case fatality rate of 2.5% is similar to that of the 2018/2019 “Spanish flu” pandemic, and higher than both the 2009 H1N1 pandemic, with a case fatality rate of 0.02, and seasonal influenza, where the average case fatality rate is estimated to be around 0.06.

It is much lower than the case fatality rate for either SARS, at about 10%, or MERS, at 30%.

In the long term, however, 2019-nCov will evolve, as viruses are wont to do. And there is a possibility of its evolving toward being either more or less lethal.

SARS evolved very rapidly, to the point that the virus responsible for the second wave of the pandemic was purely human, with no animal reservoir, and was thus eradicated when the second wave was contained via public health measures. To date, 2019-nCoV does not appear to be under the pressure that shaped SARS, and is evolving more slowly.

The next seasonal bug?

The long-term, large-scale behavior of the virus will also affect its impact.

Influenza’s effects are seasonal, and if 2019-nCoV is the same, the first wave may wane as the warmer months approach. (Or not. Why influenza’s waves come and go as they, do, McGeer said, is not understood: “There’s a Nobel Prize in there for somebody.”)

If its behavior is seasonal, the coronavirus’ waning infections may provide a literal and figurative break for public health and biomedical communities racing to develop effective containment, treatment and prevention strategies.

Another open question is the impact rate, or what percentage of the population is infected. The H1N1 pandemic had an impact rate of 30%; seasonal influenza has lower impact rates, due to pre-existing immunity.

Seasonal behavior and impact rate, McGeer said, “will make a very large difference in terms of how much trouble we’re going to be in.”

All things considered, there is “reason to hope that this will not be worse than a regular flu season,” she said, although “even if it is no worse than a regular flu season, it will be more disruptive.”

2019-nCoV, and other emerging viruses, by their nature, press “buttons where we know that we are not going to respond rationally,” she said.

The intense global public concern about the emerging epidemic is one example of such irrationality. The 2019/2020 flu season has killed roughly 8,000 Americans to date, and hospitalized 100,000 more.

In contrast, as of Feb. 5, the CDC reported 11 confirmed coronavirus cases and no deaths in the U.S.

McGeer neatly summed up the difference between the most appropriate responses for public health officials and private individuals at this point.

“People should not be behaving any differently today in the U.S. or Canada,” she said. But “that does not mean that we do not have a serious problem coming.”

Editor’s Note: This is the second of a two-part series exploring how experience with other viruses is being used to understand and rapidly respond to the emergence 2019-nCoV. Read part 1.