CNBC's Jim Cramer broke down Thursday's sell-off and explained why he thinks the coronavirus outbreak will continue to be a thorn in the market. The "Mad Money" host checked in with Domino's Pizza CEO Ritch Allison after the chain reported a domineering fourth-quarter amid a tight delivery market. Later in the show Cramer broke down why investors may want to buy the dip in Vertex Pharmaceuticals.

Investors were spooked by a pickup in coronavirus cases in South Korea and triggered a sell-off on the stock market, CNBC's Jim Cramer said Thursday.

The Dow Jones Industrial Average dropped 128 points, the S&P 500 declined 0.38% and the Nasdaq Composite fell 0.67% during the trading day, though the major averages were down even more earlier in the session.

"Breathers like this one can extend the life of a rally," the "Mad Money" host said. "But without good news on the virus, I'm pretty certain that we'll have more breathers down the pike, so be prepared."

Carryout has become a bright spot for Domino's Pizza as the restaurant chain battles in a tough, low-margin food delivery environment, CEO Ritch Allison told Cramer.

Shares of the Ann Arbor, Michigan-based pizza franchise popped almost 26% during the trading day on a strong fourth-quarter report that smashed Wall Street estimates.

"While most of the industry is running headlong into delivery, which is inherently a more profitable channel to serve, we're working hard to hold serve on that delivery side of the business while really growing that carryout channel," Allison said in a "Mad Money" interview. Carryout "is going to be an important part of the profit equation going forward."

The market gave investors an opportunity to buy position in Vertex Pharmaceuticals as drug stocks traded lower the day after the Nevada Democratic debate, Cramer said.

"Vertex Pharma got dinged today, and I think this is a very buyable dip in what's widely considered to be the hottest biotech story of the year," the host said, adding the company "accomplished something that was unthinkable not too long ago, a near-triumph over the scourge that is cystic fibrosis."

In Cramer's lighting round, the "Mad Money" host delivered his thoughts on callers' favorite stock picks in rapid speed.

General Motors: "No. I think GM is of the past. ... I think it's going to perform less in the market."

Okta: "Well look, that's a Cramer-family fave, Okta. ... It is a high flyer. [CEO] Todd McKinnon is doing a great job. I would not buy it all at once. Zscaler is down tonight. That could make Okta go lower. Maybe you pick at it that way."

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