The stock market posted a huge advance on Friday, lifted by an extremely optimistic outlook on the employment front. Most economists had expected dramatic job losses in May, but the employment report instead showed millions of new jobs created. Even with the unemployment rate still at elevated levels, that nevertheless brought a sigh of relief for market participants.

As of just before noon EDT today, the Dow Jones Industrial Average (DJINDICES:^DJI) was up 944 points to 27,226. The S&P 500 (SNPINDEX:^GSPC) rose 90 points to 3,202, and the Nasdaq Composite (NASDAQINDEX:^IXIC) picked up 207 points to 9,823.

Yet even though the overall market gained ground, there were some stocks that missed out on the rally. Among them were a couple that have done extremely well even when the broader market was struggling. For Moderna (NASDAQ:MRNA) and Slack Technologies (NYSE:WORK), shareholders seem to think that what's good for the broader economy might end up taking away from the long-term potential of their respective businesses.

Investors jump off the vaccine-play bandwagon

Shares of Moderna were down 5% Friday morning, adding to the volatility that the biotech stock has seen recently. Although the stock has tripled since the beginning of the year, it's down by a third from where it traded just three weeks ago.

Investors in Moderna are squarely focused on its coronavirus vaccine candidate, which got a vote of confidence from the White House on Thursday. Moderna's mRNA1273, which is now in phase 2 clinical trials, was one of five vaccines dubbed most likely to succeed. Other treatments include candidates from AstraZeneca, Johnson & Johnson, Merck, and Pfizer.

Yet there's still considerable uncertainty about Moderna's future. Even though some believe that the company is currently in the lead in pushing its vaccine through clinical trials, that doesn't mean that other competing vaccines won't end up proving themselves more quickly. Moreover, there's always the chance that Moderna's candidate won't be effective in preventing people from catching COVID-19, or that alternative treatments will do a better job.

Today's move lower reflects the shift among investors to look more at the stocks that have been beaten down during the coronavirus bear market. That doesn't mean Moderna is over and done with, but investors can continue to expect pauses along the way even if things keep going well for its vaccine development.

Six tiles with the Slack logo, with different colors and one with the Golden Gate Bridge.

Image source: Slack Technologies.

This stock is slacking

Elsewhere, Slack saw its stock drop 16%. The business-collaboration platform provider has seen nice gains during the pandemic, but its latest report raised concerns about its near-term prospects.

First-quarter financial numbers were solid. Revenue jumped 50% from year-ago levels, and the company reported adding 12,000 new paying customers. More than 90,000 organizations signed on with Slack on either a paid or free plan during the three months ending April 30. The number of organizations paying $100,000 or more to Slack in annual recurring revenue rose by nearly half to 963. It also sees the good times continuing. The company projects full-year revenue growth of 36% to 38%.

However, not everyone was happy that Slack chose not to provide guidance on full-year calculated billings numbers, which grew at a slower rate than sales in the first quarter. Moreover, word about a deeper collaboration between Slack and Amazon.com seemed to show that the company is having to take seriously the threat of competing products from Microsoft.

Across the market, investors seem to think that returning to normal means that stocks that have capitalized on remote work will reverse their gains. That's not inevitable, but it's what's driving shares of Slack and other tech stocks down on Friday.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.