Dozens of companies have joined the race to develop a vaccine or a treatment for COVID-19. However, many of these companies remain risky investments.

For instance, shares of Sorrento Therapeutics (NASDAQ:SRNE) soared by more than 100% in one day after the company announced it had discovered a potential cure for COVID-19. Despite this great bit of news, Sorrento Therapeutics has only one approved product that doesn't generate much revenue, a dwindling cash balance, no pipeline candidates in late-stage trials, and a long road ahead before it can even hope to launch a COVID-19 vaccine on the market. In short, investors had better avoid this particular stock.

With that said, several companies currently involved in the fight against COVID-19 deserve serious consideration based on their core businesses. Here are two that investors with cash on the sidelines would do well to consider buying today: Merck (NYSE:MRK) and Novavax (NASDAQ:NVAX)

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1. Merck 

Merck officially joined the fight against COVID-19 in late May when it acquired Themis, a privately held company that develops vaccines for infectious diseases, for an undisclosed cash payment. Thanks to this acquisition, Merck gained the rights to a vaccine candidate for the SARS-CoV-2 virus Themis was developing; the candidate in question is currently undergoing preclinical development, and Merck plans on starting clinical trials for the vaccine later this year.

Merck also teamed up with IAVI, a nonprofit scientific research organization, and with Ridgeback Biotherapeutics, a privately held biotech company. Merck is developing a vaccine for COVID-19 in collaboration with IAVI, and has acquired the rights to an investigational oral antiviral drug for COVID-19 called EIDD-2801 from Ridgeback. As part of the deal, Ridgeback received an upfront payment from Merck of an undisclosed amount and could receive more in milestone payments.

It's worth noting the Trump Administration selected Merck and four other companies as the most likely candidates to launch a vaccine for COVID-19 on the market. This initiative, dubbed "Operation Warp Speed," is meant to accelerate the development of a vaccine for the deadly disease.

Beyond its involvement in the fight against COVID-19, Merck remains one of the better pharma giants to buy. The company's cancer treatment Keytruda continues to rack up new regulatory approvals and deliver strong and growing revenue. During the first quarter, Merck's sales came in at $12.1 billion, an 11% year-over-year increase.

Nurse holding blood filled test tube for coronavirus testing.

Image Source: Getty Images.

Keytruda's sales were $3.3 billion, representing a 45% increase compared to the prior-year quarter. Further, the planned spinoff of Merck's women's health, trusted legacy brands, and biosimilars businesses should help the company focus on its better-performing segments and deliver stronger revenue and earnings growth.

Let's not forget about Merck's ability to replenish its pipeline, thanks to several collaboration agreements the company has in place. For instance, Merck partnered up with Taiho Pharmaceuticals and Astex Pharmaceuticals earlier this year. Through this partnership, Merck acquired the rights to some of Taiho's and Astex's pipeline candidates. In exchange, Taiho and Astex received an upfront payment of $50 million, with additional incentive payments of up to $2.5 billion.

While Merck hasn't performed particularly well this year, I think the pharma company is poised to make a strong comeback when the dust settles. 

2. Novavax 

Novavax has been actively working to develop a vaccine for COVID-19 for the past several months. On April 8, the company announced that it had identified a lead candidate, an antibody called NVX-CoV2373. In late May, Novavax kicked off a phase 1/2 clinical trial for NVX-CoV2373. This trial will be conducted in two phases. The first, held in Australia, will enroll 130 healthy participants and will test the vaccine's safety and immunogenicity.

The second phase will be conducted in the U.S. and several other countries, and will test the immunity, safety, and disease reduction of the vaccine in a broader age range of healthy volunteers. Novavax has received help on several occasions in its quest to develop a vaccine for COVID-19. For instance, the company received funding from the Coalition for Epidemic Preparedness Innovations (CEPI) of up to $388 million to advance the clinical development of its investigational COVID-19 vaccine.

Novavax has other promising pipeline candidates. In particular, the company's NanoFlu vaccine, a potential flu vaccine for adults over 65, could be a big winner. This vaccine proved more effective than Sanofi's (NASDAQ:SNY) Fluozone HD -- the current market leader -- in a clinical trial. And with recent positive results from a phase 3 study for NanoFlu, Novavax is gearing up to submit a Biologics License Application to the U.S. Food and Drug Administration. I think Novavax's NanoFlu will likely earn regulatory approval, and it will help the company's financial results improve. However, before investing in this biotech company, there are two major caveats to consider.

First, one of Novavax's peers could launch a COVID-19 vaccine on the market. If that happens, Novavax's stock could come crashing down. Second, Novavax is currently an expensive stock. The company is trading at more than 300 times its future sales. For those reasons, I think Novavax is a risky stock at the moment, but for those who can stomach the risk, the company is worth considering. If all goes well for Novavax, its shares will continue to outperform the market and reward its shareholders in the process.