The stock market continued to gain ground on Thursday, picking up greater momentum as investors started to get more comfortable with the idea of a full economic recovery. Even with bond yields soaring, major stock market indexes built on their rise from Wednesday. The Dow Jones Industrial Average (DJINDICES:^DJI), S&P 500 (SNPINDEX:^GSPC), and Nasdaq Composite (NASDAQINDEX:^IXIC) all posted gains in the neighborhood of 1%.

Index

Daily Percentage Change

Daily Point Change

Dow

+0.98%

+338

S&P 500

+0.83%

+36

Nasdaq

+1.05%

+152

Data source: Yahoo! Finance.

The fight against COVID-19 has been long and difficult, but some companies have made names for themselves in the midst of the pandemic. A couple of stocks that have played instrumental roles with COVID posted big gains in after-hours trading on Thursday, and what they're saying about their businesses could have implications for the whole stock market. Below, we'll look at why Quidel (NASDAQ:QDEL) and Vaxart (NASDAQ:VXRT) moved sharply upward late Thursday afternoon.

Medical professional holding swab and test tube marked COVID-19.

Image source: Getty Images.

Quidel passes the test

Shares of Quidel were up less than 1% in the regular trading session on Thursday, but the stock moved higher by nearly 7% as of 6 p.m. EDT after hours. The rapid-testing specialist reported preliminary numbers for the third quarter that impressed investors.

Quidel's results showed the continued demand for the company's test products. Total revenue is likely to come in between $505 million and $510 million, which would be 6% to 7% higher than it was in the year-ago period. COVID-related sales for the period should be around $406 million, which would mark growth of about 8% year over year.

Quidel said that it has seen a huge boost in orders for its tests for the virus that causes COVID. The company shipped more than 45 million tests during the third quarter of 2021, and that's well over double the number from the same period a year ago. CEO Douglas Bryant attributed the rise to the spread of the delta variant, and he credited his company's moves to meet demand at multiple points of care in order to boost sales.

Deals like Quidel's 12-month $284 million contract to supply more than 50 million QuickVue At-Home over-the-counter rapid antigen tests to the federal government will be crucial in sustaining growth. Yet the company has worked hard to build production capacity to meet demand, and that bodes well for its immediate future.

Vaxart gets a vote of confidence

Meanwhile, shares of Vaxart jumped almost 10% in after-hours trading. A study of the company's oral COVID vaccine candidate showed encouraging results that could prompt further development.

Duke University led a study to see whether Vaxart's investigational oral-tablet vaccine would reduce airborne transmission of the virus causing COVID in animals. The results supported the conclusion that taking the vaccine reduced the subsequent transmission of COVID, even when vaccinated subjects saw infection breakthrough.

Vaxart believes its vaccine is important because existing COVID vaccines still allow vaccinated individuals to be carriers for airborne transmission. By providing for less viral shedding, Vaxart's vaccine candidate could offer a different kind of protection for public health.

Some are concerned that the timeline for Vaxart's pill might be too long to compete against oral antivirals and other COVID solutions. Nevertheless, bullish investors this afternoon think there's more than enough room for innovation of all kinds, and they're hopeful that Vaxart could help carry the ball further.

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.