Amazon confronts pandemic costs as cloud computing and investments help bottom line.

An improving economy and a persistent virus are beginning to weigh on Amazon’s retail business, as its cloud computing business grew and an investment lifted profits.

The company, whose profits, employee count and share price swelled two years ago as Covid forced people to stay home, said on Thursday that its operating income in the fourth quarter tumbled to $3.5 billion, about half the $6.9 billion it earned in the fourth quarter of 2020.

But net income, which was also expected to fall, rose sharply owing to what Amazon called a “pre-tax valuation gain” in Rivian Automotive, an Amazon investment that went public in the fourth quarter. Amazon owns about 20 percent of the electric vehicle maker. Net income increased to $14.3 billion, compared with $7.2 billion a year ago.

That helped set off a sharp rise in Amazon shares in after-hours trading, quickly pushing them up about 17 percent. During regular trading, as investors fretted over what was to come, shares fell 8 percent.

“As expected over the holidays, we saw higher costs driven by labor supply shortages and inflationary pressures, and these issues persisted into the first quarter due to omicron,” Andy Jassy, Amazon’s chief executive, said in a statement.

Amazon controls about 40 percent of the e-commerce market and there was still plenty of demand in the quarter, always its biggest of the year. Revenue rose to a record $137.4 billion, just slightly under what analysts were expecting.

AWS, Amazon’s cloud division, racked up its usual impressive performance, with operating income rising 49 percent.

To compensate for its increased costs, Amazon said it was raising the annual price of its Prime shipping club to $139, from $119. The company said it was the first increase since 2018.