What happened

America's stock market caught a bad case of coronavirus today. Shares of Amazon.com (AMZN -1.11%) stock fell 4.1%, while Alphabet (GOOG 0.64%) (GOOGL 0.53%) closed the day down 4.3%. Meanwhile, Advanced Micro Devices (AMD 0.48%) stock was down 7.8%.

Worse, this sell-off wasn't limited to companies beginning with the letter A. It's infecting pretty much all of the stock market. By close of trading on the New York Stock Exchange, the Dow index of America's biggest blue chips sank 3.6%, while the Nasdaq closed 3.7% lower, and the broader S&P 500 was off 3.4%.

A gloved hand holds a plastic tube labeled coronavirus.

Image source: Getty Images.

So what

Over the weekend, media reported that COVID-19 coronavirus had spread to locations including Iran, Italy, and South Korea. Some 77,150 people are now reported to be infected in China, with thousands more suffering from the disease outside China's borders, according to a count maintained by Johns Hopkins University.  

Investors are beginning to understand that a pandemic just might be bad news for everything from selling advertisements (Alphabet) to selling stuff (Amazon) to selling a particular type of stuff (computers). As a result, a lot of the gains these stocks had been racking up recently began evaporating today.

Now what

Will the panic pass, and stock prices recover? Eventually, sure. (I'd bet money on it.)

That being said, it's hard to say how long this sell-off might last, and how long we might need to wait for a more positive market to return. In the meantime, I have to say that I'm a whole lot more sanguine about buying Alphabet shares at 29 times earnings than I am about buying either Amazon at 88 times earnings -- or AMD at 166.5.

Whether you're with me on that or not, now's probably not a great time to sell these stocks. When buyers are in such short supply, you're unlikely to get the best prices for your shares. Moreover, after such a big sell-off today, there's a better than average chance that tomorrow will be better (he said, hopefully) as short-sellers capitalize on newly cheap shares to close their positions -- adding buyers, and better prices, to the market tomorrow.

In the meantime, now is a great time to start digging through the rubble and checking to see if any of the stocks on your shopping list have finally gotten cheap enough to buy.