The severity of the new coronavirus — how many people might die from the viral infection — is the biggest question surrounding the outbreak, a panel of public health researchers said at the American Association for the Advancement of Science’s Annual Meeting in Seattle.

One way to measure severity is to divide the number of deaths by the number of confirmed cases of a disease. As of Feb. 13, there was a 3% risk of death under this calculation, with 1,369 reported deaths, said Scott Dowell, deputy director in vaccine development & surveillance at the Bill and Melinda Gates Foundation.

“This is one of the most threatening outbreaks that I’ve seen in my career,” Dowell said.

Both the number of deaths and number of cases from the new virus, named COVID-19, are likely to rise, he warned. In fact, Dowell’s Feb. 13 calculations were based on 46,997 lab-confirmed cases. Reports now suggest that the number of cases surged overnight to more than 63,000.

Severity remains uncertain, said Dowell. “The reason is that at this stage of a rapidly expanding outbreak, to put it bluntly, most people haven’t had the time to die,” he explained. “The big bulk of cases … have been infected recently. The median time from exposure to death in the early cases was 18 days. So, most have not had time to resolve their case or to die.”

Dowell said it is possible that there may be a large number of mild cases of coronavirus that are undetected. If there is a hundred-fold underestimate in the number of cases, the severity of the outbreak would be similar to the 1957 pandemic influenza, which killed an estimated 1.1 million people worldwide.

“If it’s five-fold underestimated, as some have projected, that’s much more concerning because that puts it in the range of 1918, which was the worst pandemic in recorded history,” said Dowell. The 1918 influenza pandemic killed an estimated 50 million people across the globe.

Researchers including Trevor Bedford have been tracing the genetic changes in the new coronavirus over time. The data can be used to estimate the total number of cases, he said.

Bedford, a Fred Hutch associate member in the vaccine and infectious disease division and the computational biology program, noted that genomic data suggest there may be a ten-fold underestimate in the total number of cases. “So that would push things more to the severe side.”

Some of these uncertainties about the virus have persisted because “China is not open and transparent,” said Jon Cohen, a senior correspondent for Science. “If you watch WHO’s press conferences or the U.S. CDC’s press conferences, Hong Kong has done this as well, they’re daily, they’re open, journalists get to ask questions … that’s not happening out of China, and my sources in China are largely reluctant to speak.”

Viral family trees built from genomic data have helped trace the new coronavirus’ origin in bats through an unknown intermediate animal to humans, Bedford said. Researchers around the world are tracking the virus’ genetic changes in near real-time, from its leap to humans between Nov. 15 and Dec. 15 last year, after which human-to-human transmission took hold.

At the moment, 2.5 people on average are infected per coronavirus case, meaning that it is “robustly transmitted,” Dowell said.

Bedford said scientists are contributing new genetic sequences to the open-source project nextstrain.org so rapidly that in some cases, there are only three to six days between collecting a new viral sample and uploading its sequence. “We can actually use this genomic data in a much more actionable fashion to understand things as they’re occurring rather than just retrospectively.”

Jaime Yassif, a senior fellow for global biological policy and programs at NTI, warned that “the world is not prepared to prevent and respond to pandemics on a global scale,” citing the findings of an NTI report on global health security.

Gaps in global pandemic preparedness were identified after the 2014 West Africa Ebola outbreak, she said, “but we haven’t seen sustained political will and incentives to spend money and time filling those gaps.”