In recent days, some public health experts and scientists have begun uttering the P-word in reference to a surging outbreak of the new coronavirus that’s already infected at least 24,000 people and killed over 400: pandemic. But when will we know if the Wuhan coronavirus, known as 2019-nCoV, has spread far and wide enough to become one?
Using the simplest definition, the thing that most determines a pandemic is the scale of the outbreak, according to Brandon Brown, an epidemiologist at University of California Riverside.
“A pandemic is an epidemic of worldwide proportions and, in the case of a virus, most people do not have immunity to the virus,” Brown told Gizmodo.
While past pandemics, like the Black Death in the 14th century and the 1918 influenza, have gained notoriety for decimating the world’s population, the lethality of an outbreak isn’t really important for deciding whether it’s a pandemic. The fact that 2019-nCoV may only kill 2 percent of victims (and possibly even less than that, if many milder cases aren’t being detected) doesn’t disqualify it from becoming a pandemic.
Cases of 2019-nCoV, which causes respiratory illness and pneumonia in its victims, have been documented in at least 25 countries, including the U.S. But right now, the epicenter of the outbreak remains in China. And though we’re starting to see isolated cases of human-to-human transmission in other countries, indicating its potential to spread farther, the other shoe has yet to drop. The majority of out-of-China diagnoses (over 150, as of February 4) have so far involved people who caught the virus while traveling in China.
“Experts at the WHO have said that the novel coronavirus is not a pandemic, but rather an epidemic with multiple foci, since the number of cases outside of mainland China are few,” Brown noted, referring to a statement made Wednesday by Silvie Briand, director of the WHO’s global infectious hazard preparedness program.
There isn’t a set number of countries where an outbreak is spreading that must be reached before the World Health Organization pulls the pandemic alarm. But if the number of cases continue to rise, and especially if evidence of sustained human-to-human transmission in countries outside of China shows up, the WHO may decide to change their mind, similarly to how they revisited their decision to declare the outbreak a global health emergency last week, Brown added.
There are still many unknowns about 2019-nCoV that would give us a better sense of how likely a pandemic could be. We don’t know if the virus can be transmitted from someone before their symptoms start or from someone who never gets sick at all, though a recent report suggesting asymptomatic transmission had happened in Germany was debunked this week. And we only have a rough sense of how contagious the virus could be.
Early reports have estimated that the virus’s R0 (pronounced R “naught”), a measurement for how many other people on average are infected by a single sick person in a completely vulnerable population, is higher than the last pandemic, which occurred in 2009 and was caused by a strain of influenza. But R0 is a deceptively complex number to pin down, and experts have warned that it will take months to figure that number out for 2019-nCoV. A higher R0 value doesn’t necessarily mean an outbreak will become a pandemic, though.
The current estimated range of 2019-nCoV’s R0—somewhere in the low 2s—is still lower than that of SARS, which saw anywhere from two to five new cases per every infected victim at first. SARS ultimately petered out within six months, causing 8,000 cases and nearly 800 deaths. The drastic—and at times criticized—interventions countries have undertaken to limit the spread of 2019-nCoV, such as travel bans to and from China and quarantines of travelers, could still make it possible to halt its global spread, Brown said.
But while SARS was likely more deadly, the sheer number of Wuhan virus cases could lead to a larger death toll by the end. Even if the new coronavirus doesn’t turn into a pandemic, there’s also the possibility it could become yet another disease that routinely sickens and sometimes kills people. The fear and paranoia the virus has stoked is already taking a toll on the world.
Many variables could change in the days and weeks to come that could turn this outbreak into something much worse. But for the time being, if you’re living outside China, it’s not time to panic about the coronavirus.
“People living in the U.S. should still not be worried,” Brown said. “There are only 11 known cases of the novel coronavirus in the U.S., while we now have nearly 20 million ill with influenza in the current flu season and at least 10,000 deaths from the flu this flu season.”