A combination of factors—including fourth quarter 2019 profits that missed Wall Street expectations—led to the stock hit. But the latest coronavirus outbreak in China is also holding back AstraZeneca’s 2020 financial outlook.

“All guidance assumes an unfavorable impact from China lasting up to a few months as a result of the recent novel coronavirus (Covid-19) outbreak,” the company wrote in its latest earnings report.

In the final quarter of 2019, Astra’s core operating profit fell 29% to $1.55 billion while rising 13% to $6.44 billion for the full year, falling short of estimates.

As for the coronavirus effect, it’s not hard to see why the outbreak may have an outsized effect on AstraZeneca’s business. China is becoming a larger and larger share of the company’s revenue pool as more AZ products, such as the popular cancer treatment Lynparza, are approved for more uses in the country.

In 2019, China constituted $4.9 billion out of the firm’s $8.2 billion (nearly 60%) in products sales from emerging markets, and nearly 21% of total product sales.

The supply chain disruptions wrought by Covid-19 and the difficulty of moving inventory into China has AstraZeneca executives actively monitoring the severity and length of the current outbreak.

In its earnings presentation, the company stated it expects the outbreak to hit its sales numbers for “up to a few months”—but it could easily last longer. And that could change 2020 from a year of double-digit revenue growth for AstraZeneca to a single-digit one.

More must-read stories from Fortune:

—Can you catch it twice? Answers to 5 pressing coronavirus questions
—Why China is still so susceptible to disease outbreaks
—Bernard Arnault was briefly the world’s richest man. Then coronavirus struck
—Will summer kill the coronavirus?
—My boss wants me to travel during the coronavirus. Do I have to go?

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