As the new coronavirus continues to cross international borders, the two key questions on public health officials’ minds are: “How deadly is it?” and “Can it be contained?”
The two outbreaks that give the most insight into these questions are the 2002-2003 SARS outbreak, which spread from China to 26 other countries but was contained after eight months, and the 2009 H1N1 influenza pandemic, which originated in Mexico and spread globally despite all containment efforts.
The severity and mortality of a novel emerging virus -- which scientists are calling 2019-nCoV -- are very difficult to judge when new data is coming in on a daily basis.
During the 2009 influenza pandemic, earliest reports suggested an extremely high case fatality of 7%. However, the initially reported information was a gross underestimate. This was simply due to a much larger number of mild cases that were not reported to any health system. After several months -- when pandemic data had been collected from many countries experiencing an epidemic wave -- the 2009 influenza turned out to be much milder than was thought in the initial weeks. Its case fatality was lower than 0.1% and in line with other known human influenza viruses.
The case fatality for SARS, during its eight months of circulation, was just under 10%.
Is the current epidemic more similar in severity and transmissibility to the SARS outbreak or the 2009 flu pandemic? We do not yet have enough solid evidence to answer this question. I am optimistic that the scientific community’s sharing ethos and rapid data analytics will soon generate the data needed.
During these early stages of the outbreak investigation, it is difficult to estimate the lethality of this new virus.
So, with all of this uncertainty, how much effort should public health officials put into containment, quarantine, and isolation activities? Should all airports be implementing temperature screening for incoming passengers? There are no easy answers, as there are only a few historical examples to look back on, and none of them is guaranteed to be a template for the 2019-nCoV epidemic.
Fortunately for human beings, a pathogen like 2019-nCoV cannot have its cake and eat it, too. The virus cannot be both deadly and undetectable.
With a more severe symptoms profile, a respiratory infection will have more sudden onset, earlier symptoms, a higher chance of severity and death, and it will probably cause patients to report to hospitals at an earlier stage of infection. An outbreak of a respiratory virus like this will typically be deadly but containable.
With a less severe symptoms profile, patients may stay in an asymptomatic or mildly symptomatic state for a long time, symptoms appearance may be more gradual than sudden, and progression to hospitalization and death would be rare. An infection like this is difficult to detect and thus difficult to control, but fortunately it is much less lethal.
A key characteristic to examine in these two disease profiles is whether symptoms appear before transmissibility, ie at a point when patients are not yet able to infect others, or the other way around. For SARS, symptoms usually appeared before transmissibility. This feature made SARS containable.
For the 2009 H1N1 pandemic, transmissibility appeared about one day before symptoms. This meant that even the best control measures missed 20% of transmitting patients, simply because they showed no symptoms.
For the 2019-nCoV epidemic, it appears that individuals can transmit the virus before being symptomatic. However, at this early stage, this is far from certain.
Can a pathogen like this have its international spread controlled? Will airport screening and isolation of febrile cases be effective at slowing down the initial outbreak or perhaps containing it entirely?
At this moment, 2019-nCoV looks like its severity and transmission profile are somewhere between SARS and the 2009 H1N1 influenza.
If this is accurate, airport screening, case isolation, contact tracing, and social distancing efforts may be enough in some cities to delay or fend off the arriving stream of new cases. In the next month or two, we will see how easily newly introduced seed cases are able to establish local epidemics outside the Chinese mainland.
With a little luck some cities may be able to control their outbreaks. With open scientific collaboration, we may learn which containment strategies work best, in preparation for our next pandemic later this decade.
Maciej F Boni is an Associate Professor of Biology, Pennsylvania State University.
