Following a tumultuous three-and-a-half-hour-long trading session the day after Thanksgiving, U.S. stocks posted a hearty rebound Monday. The S&P 500 climbed 1.32% to $4,655.27, while the technology-stock-filled Nasdaq 100 rose 2.33% to $16,399.24. And volatility dramatically subsided after surging to levels not seen in months on Friday, as well. The Cboe Volatility Index, or VIX, which is often referred to as the stock market’s fear gauge, declined 19.78% during the latest trading session.

Monday’s gains came alongside a series of optmistic, though preliminary, forecasts about the newest mutation of the COVID-19 virus, which the World Health Organization declared just a few days ago to be a variant of concern. So far, there have been few indications that Omicron causes a more severe infection than other versions of the virus. Vaccine makers BioNTech and Pfizer have said they can adapt their mRNA vaccine to address the Omicron variant—if it does not already—and roll it out within 100 days. And President Joe Biden looked to address widespread worries Monday about another impending lockdown, saying he was not considering anything of the sort at the moment.

Anxiety has crept back onto Wall Street, nonetheless.

With no definitive clarity about Omicron’s transmissability, severity, or resiliency against vaccines—and with little clarity on the nearterm horizon—investors and traders are still preparing for what could be a bumpy few weeks heading into 2022. Uncertainty has long been billed as the main foe of markets, after all. “It’s still very, very early,” Randy Frederick, managing director of trading and derivatives for the Charles Schwab Center for Financial Research, says of the Omicron variant.

Unease among investors spiked Friday, as the mutation caused countries in Europe and Asia to begin restricting travel. The VIX posted its fourth-largest jump in a single day ever. In the abbreviated trading session that lasted half a day Friday, more than 9 billion shares were traded in the U.S., according to Cboe Global Markets data. On a typical, full-length trading day, somewhere between 10 billion and 11 billion shares are usually traded.

Options trading was even more frenetic, with volumes reaching a half-day record of 38.8 million contracts traded, according to Cboe senior director and head of product intelligence Henry Schwartz. And much of the trading in U.S. stocks followed the tried-and-true pandemic playbook of dumping travel companies and others that were hit early on by COVID-19 while snatching up shares in work-from-home companies, Schwartz told Fortune, adding, “We’ve seen this movie before, right?”

In a research report, BlackRock strategists wrote that the newest variant has the potential to trigger a rethinking in the markets on growth-focused companies, hit risk sentiment, and adversely impact service sectors. The fallout could be even more dramatic if vaccines and treatments are not effective, the asset manager’s team warned in the Nov. 29 report.

If vaccines and treatments are effective against Omicron? According to BlackRock, “We don’t see it changing the otherwise solid picture for equities: a powerful restart and the prospect of continued low real rates.”