What happened Quidel (NASDAQ: QDEL) stock was popping on Friday with shares jumping 11.3% as of 11:02 a.m. ET. The impressive gain came after the company announced its 2021 fourth-quarter and full-year results following the market close on Thursday. The diagnostics testing company reported fourth-quarter revenue of $636.9 million. Although this reflected a sharp 21.2% year-over-year decline, it still narrowly topped the consensus estimate. Quidel also posted adjusted Q4 earnings of $7.29 per share. This result was much lower than adjusted earnings of $11.07 per share in the prior-year period. However, it blew past the average analysts' estimate of $4.89 per share. So what It might be surprising at first glance to see Quidel's steep revenue and earnings declines along with a surge for the life sciences stock. But this move underscores just how much stocks are driven by expectations. There was one main reason behind those negative year-over-year comparisons. Sales for Quidel's Sofia 2 Flu + SARS antigen fluorescent immunoassay plunged by $249 million. While the company's QuickVue COVID-19 products picked up some of the slack, they have lower margins. COVID-19 continued to be the big story for Quidel in the fourth quarter of 2021. Revenue for its COVID-19 products totaled $511.8 million, up from $405.3 million in the prior-year period. Image source: Getty Images. Now what Quidel's fortunes will depend largely on COVID-19 for the immediate future. The good news is that CEO Douglas Bryant said in the company's press release that the "demand for COVID-19 testing remains elevated" in the early months of 2022. However, there are other growth drivers for Quidel on the way. The company is gearing up for the U.S. launch of its Savanna multiplex molecular platform. This platform enables testing of as many as 12 pathogens from a single sample in under 25 minutes. Quidel also hopes to close on its acquisition of Ortho Clinical Diagnostics in the first half of this year. 10 stocks we like better than QuidelWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and Quidel wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of January 20, 2022 Keith Speights has no position in any of the stocks mentioned. The Motley Fool owns and recommends Quidel. The Motley Fool has a disclosure policy.Source