Shares of Moderna (MRNA 1.69%) were jumping 9.5% higher as of 11:09 a.m. ET on Thursday after rising as much as 10% earlier in the day. The gain came after the biotech company announced its fourth-quarter and fiscal year 2023 results.

The big news in Moderna's Q4 update was a surprise profit of $217 million, or $0.53 per share, based on generally accepted accounting principles (GAAP). The average analysts' estimate was for a Q4 loss of $0.90 per share.

Moderna also reported Q4 revenue of $2.8 billion, down from $5.1 billion in the prior-year period. However, this result was well above the consensus revenue estimate of $2.3 billion.

How did Moderna beat estimates so handily?

Moderna's Q4 revenue was better than Wall Street expected, primarily due to international sales of the company's Spikevax COVID-19 vaccine. Over 71% of total Spikevax sales stemmed from outside the U.S.

However, Moderna received some extra help in Q4. Around $600 million of the $2 billion recorded in international sales for Spikevax was due to the company recognizing deferred revenue related to Gavi, the Vaccine Alliance.

This higher revenue was a key factor behind Moderna's unexpected profit in Q4. That wasn't the only reason, though. Moderna's bottom line was also boosted by an income tax benefit of $147 million.

Is Moderna stock a buy now after its Q4 update?

I don't think Moderna stock is a buy solely because of its Q4 results. My view is that risk-averse investors will be better off going with other stocks.

However, aggressive investors could find Moderna appealing right now. The company hopes to win U.S. regulatory approval for its respiratory syncytial virus (RSV) vaccine soon. It's also optimistic about filing for approval of seasonal flu vaccine mRNA-1010 this year. I predict Moderna's future will be brighter than its recent past.