The World Health Organization (WHO) said earlier this week that the global coronavirus death rate had reached 3.4%, significantly higher than what the mortality rate is for seasonal flu. But, as with so many public health indicators in a rapidly evolving situation, that number comes with numerous caveats.

The 3.4% figure, per the WHO’s own officials, is a crude estimate. It’s also the first percentage that covers worldwide deaths related to the novel coronavirus and COVID-19, rather than just China, where the outbreak originated.

The coronavirus mortality rate is expected to shift significantly in the coming weeks and months as global health officials gather more data.

Some of the hangups? The difficulty of pooling information from dozens of countries now experiencing novel coronavirus cases and the tardiness of testing in certain nations—including in the United States. The U.S. has had manufacturing issues with certain tests developed by the Centers for Disease Control (CDC) and had only reported 99 total cases and 10 deaths related to COVID-19 across 13 states as of Thursday.

“I think the mortality is going to end up at 1% or below, more consistent with the H1N1 flu outbreak of 2009,” Geoff Porges, director of therapeutics at SVB Leerink, told Fortune.

How does that work? For one, under-testing across multiple nations winds up increasing the mortality rate. There may actually be hundreds or even thousands of more people who have coronavirus but haven’t died from it—which means that only the most severe cases, which may lead to deaths, are being recorded and monitored.

“It’s almost guaranteed that we’ll see a drop in the mortality rate,” said Porges.

Porges also recently sat down with former Food and Drug Administration (FDA) commissioner Scott Gottlieb to discuss the coronavirus outbreak. The conversation was encouraging despite the current testing woes.

“Overall Dr. Gottlieb believed that the actual number of U.S. infections is likely far higher than is currently reported, however he believes the mortality rate in the U.S. is likely to be lower than in other less-developed parts of the world,” SVB Leerink wrote in a note describing the one-on-one conversation.

More must-read stories from Fortune:

—Testing for coronavirus should be free, but it’s not always that simple
—Coronavirus is mutating: Chinese scientists find second strain
—Coronavirus is giving China cover to expand its surveillance. What happens next?
—The coronavirus is officially claiming its first corporate casualties
—Why the U.S. is so far behind other countries in coronavirus testing
—Travel insurance is booming, even though it doesn’t help flight changes and cancellations
—Six states are still not testing for coronavirus

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