Equity markets performed well in January, as they often do, but as the dust settles on that early-year run, the strategy for long-term investors remains the same: Invest in companies that can perform well over long periods, whether or not they moved in tandem with the market in January. One month of strong (or poor) returns means little in the grand scheme of things.

To illustrate that point, let's discuss two stocks in the biotech industry that have moved in opposite directions so far this year: Vertex Pharmaceuticals (VRTX -2.46%) and Moderna (MRNA -3.00%). Here's why these two companies could both produce outsized returns to patient investors.

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1. Vertex Pharmaceuticals

Vertex Pharmaceuticals is starting the year strong. On Jan. 30, the company announced that the U.S. Food and Drug Administration had approved Journavx, the first non-opioid oral pain signal inhibitor to earn the green light from regulators. Vertex's shares jumped on the news, and with good reason. Considering the devastation that opioids have caused in many communities in the U.S., a pain treatment that sidesteps the potential side effects of opioids fills a significant need.

Further, Vertex now has medicines approved across pain, sickle cell disease (SCD), transfusion-dependent beta-thalassemia (TDT), and, of course, cystic fibrosis (CF), its core area of expertise. Vertex still generates most of its revenue from its CF franchise and still delivers excellent financial results. In the third quarter, the company's revenue increased by 12% year over year to $2.77 billion.

In the next two years, sales from Vertex's newer medicines, including Journavx, its next-gen CF therapy Alyftrek, and Casgevy, which treats SCD and TDT, should ramp up significantly and help improve its already strong sales growth. Further, Vertex will likely make plenty of clinical progress, too. The company's late-stage pipeline includes inaxaplin, a potential therapy for APOL-1 mediated kidney disease, and povetacicept, an investigational therapy for Iga nephropathy (a chronic kidney disease).

There are no approved treatments that target the underlying causes of both of these conditions. Vertex Pharmaceuticals has more candidates in early-stage studies. There is still plenty of upside left for Vertex Pharmaceuticals, which makes it a top biotech stock to buy this month and hold onto for a while.

2. Moderna

Moderna is a victim of its own success. The biotech was fairly unknown in 2019, but rose to prominence in 2020 when it successfully developed a vaccine for COVID-19, a project in which most other companies of any size failed. Moderna made a small fortune thanks to this achievement, but its financial results and share price have been moving in the wrong direction for the better part of three years as the pandemic receded. Still, there are good reasons to expect the company to deliver strong returns over the long run.

For one, Moderna demonstrated its innovative capabilities by quickly developing a COVID-19 vaccine when the world needed it most. The company's mRNA platform looks highly exciting, especially considering there are many infectious diseases for which there still aren't any vaccines, and those of the mRNA variety are faster to develop. That should grant Moderna an advantage as it seeks to create new products.

The company has already earned approval for another one, mRESVIA, a vaccine for the respiratory syncytial virus. It also produced positive phase 3 results for its combination coronavirus/flu vaccine. Moderna's potential candidate for the cytomegalovirus is currently in phase 3 studies, as is its investigational personalized cancer vaccine that delivered excellent results in phase 2 clinical trials.

This cancer vaccine, in combination with Merck's famous drug Keytruda, slashed the risk of recurrence or death in melanoma patients by 49% compared to Keytruda alone. Moderna has several other exciting candidates in phase 2 studies. Though the stock remains down, Moderna should record excellent pipeline and regulatory progress in the next few years, leading to stronger financial results. So, investors should strongly consider the stock this month while it is still struggling.