Nearly 400 private companies raised $142.5 billion by going public on the U.S. stock exchange by mid-December 2021, according to data from Renaissance Capital, an IPO institutional research and investment product company. That’s more funding than companies have ever managed to raise in a 12-month period.

The stream of public debuts was near-constant: Affirm, ThredUp, Coursera, Oatly, Bumble, Duolingo, Rent the Runway, Rivian Motors, Robinhood, to name a few, all listed shares—with the backdrop of a bloated valuation environment and soaring stock market.

“That clearly makes it attractive for companies to consider a public listing, versus other alternative methods of accessing capital,” says Rachel Gerring, IPO Leader at EY Americas, of the hefty valuations companies have obtained this year. Only a few years ago, tech companies were struggling to maintain the private valuations they secured from venture capitalists and private equity firms on their way into the public market. A 2016 McKinsey report indicated that unicorns were staying private longer as a result.

There’s also the boom in SPACs, or special purpose acquisition companies, which have made it quicker and simpler to list on an exchange—and more accessible to smaller companies. SPACs have really only become a popular means for companies to go public in the last few years, despite being an available method for a couple decades. Nearly 150 blank check companies had listed on a U.S. exchange by December 8, according to an EY IPO report.

But as 2021 comes to a close, it’s looking like the IPO boom is over, at least for now.

The stock market has become more erratic in recent weeks, which could be stemming from concerns about the highly contagious Omicron variant, inflation that has persisted for longer than expected, labor shortages, and breaks in the supply chain. Whatever the reasons, performance for newly listed companies has suddenly been quite spotty. A Fortune analysis from earlier this month showed that more than half of the 100 largest IPOs this year were trading below their initial offering price. 

“That does not bode well for those who are looking to go public,” says Gerring, who notes companies may be tempted to push back planned listings. “I don’t think it itself shuts down the market, but it certainly influences the market.”

S-1 filings have slowed to a trickle since the beginning of this month. Although there are still some private companies in transit to the public markets (one of the most notable on the agenda being Reddit, which recently said it had confidentially filed a draft registration statement with the SEC).

For those companies that do make it to the public markets in 2022, however, they may find themselves wishing for the good old days of pandemic-ridden, inflation-plagued 2021.