Investors have been worried about the coronavirus outbreak as it spreads in China and across the world, and Friday morning's stock market action clearly reflected rising levels of fear. As the number of cases moved toward the 10,000 mark, market participants increasingly believe that the outbreak won't simply die out the way similar diseases have in the past. As of 11 a.m. EST, the Dow Jones Industrial Average (DJINDICES:^DJI) was down 387 points to 28,473. The S&P 500 (SNPINDEX:^GSPC) fell 37 points to 3,246, and the Nasdaq Composite (NASDAQINDEX:^IXIC) was lower by 83 points at 9,215.

Even with health worries overhanging the market, not all of the news was bad. Amazon.com (NASDAQ:AMZN) soared after a strong earnings report. Yet in the biotech realm, Amgen (NASDAQ:AMGN) wasn't able to satisfy investors even after what looked like solid results in its most recent quarter.

A prime day for Amazon shares

Amazon.com saw its stock jump 9% after the e-commerce and cloud computing giant reported its fourth-quarter financial results. Investors were generally impressed with the numbers and with Amazon's outlook for the future.

Fleet of about 200 Amazon Prime vans.

Image source: Amazon.com.

Amazon saw sales jump 21% year over year, with particularly strong results in the North American side of the e-commerce business as well as Amazon Web Services. Earnings gains of 7% were somewhat less impressive, but that partially reflected all the investment in building out one-day delivery capabilities. The number of Prime members topped the 150 million mark. Subscription and third-party seller services were also notably strong from a growth standpoint.

Investors even seemed satisfied with predictions for falling operating income in the near future. Much of the change is tied to accounting treatment of server-related depreciation, which few shareholders really follow all that closely.

Today's move pushed Amazon's market cap back above the $1 trillion mark and was particularly impressive on a sharply lower day on Wall Street. Right now, Amazon seems to have all the momentum it needs to sustain growth for the foreseeable future.

Amgen predicts a tough 2020

Elsewhere, shares of Amgen were down 6% following its release of its fourth-quarter financial report. Despite better-than-expected numbers, investors weren't excited about future prospects for the biotech giant.

Amgen's results were somewhat mixed. Revenue in the fourth quarter of 2019 fell 1%, as biosimilar and generic competition ramped up against some of its key products. That capped a year in which the top line dropped 2%. Yet despite higher operating expenses, adjusted earnings per share were up 6% compared to the year-earlier period, buoyed by stock buybacks that lowered outstanding share counts.

Yet what shareholders really seemed not to like was Amgen's guidance. The company expects total revenue of $25 billion to $25.6 billion in 2020, with adjusted earnings of $14.85 to $15.60 per share.

The real question facing Amgen is whether recent major acquisitions will pay off with higher sales and profits. If so, then an attractive valuation could make the biotech stock seem like a steal at current levels. But if those strategic moves fail to bear fruit, then it could cause even more problems for Amgen shareholders in the future.