Despite the tremendous success of vaccines against the coronavirus, there's always more work to be done when it comes to reducing the risks associated with infection. And if the billions of dollars brought in by vaccine companies like Moderna didn't give it away, the market for coronavirus prevention and treatment is absolutely massive.

If coronavirus vaccine development was the story of 2020, antiviral pill development might well be the story of 2021 and 2022. Let's dive in and examine three of the most advanced pill makers to see what's going on, and when shareholders might see sales start to register.

A doctor shows a bottle of pills to a patient while holding a clipboard.

Image source: Getty Images.

1. Pfizer

Pfizer (PFE -1.05%) is currently working on an antiviral pill for COVID-19 to add to its profitable coronavirus portfolio, where its highly successful vaccine is front and center. The medication is currently in phase 2/3 clinical trials; it's intended for use as a preventative therapy for people who are likely to be exposed to the coronavirus by infected relatives or housemates.

The goal of Pfizer's pill is to protect people from developing symptoms of an infection with the coronavirus, even if they test positive. If the project is successful, it's likely to massively reduce or eliminate the burden of self-isolation for people exposed to the virus. Therefore, it would be a product with wide appeal to consumers, and it might also reduce their risk of developing severe disease if administered early enough.

There are a couple of caveats for investors, though. At the moment, it's unclear how much money Pfizer might make from its antiviral medication. And a purely preventative pill might have some of its market share cannibalized by the company's smash-hit vaccine, which is also preventative. Or it might have to fight for the anti-coronavirus pill market against a powerful competitor -- specifically, the next company below.

2. Merck

At the start of October, the pharma giant Merck (MRK 0.25%) announced that its investigational antiviral drug called molnupiravir appeared to be highly effective at reducing the risk of hospitalization and death for patients with mild to moderate COVID-19. The interim analysis of the drug's phase 3 clinical trial indicated that it could slash the risk of these severe outcomes by as much as 50%.

Merck has already applied for an Emergency Use Authorization (EUA) from the Food and Drug Administration (FDA), and it could hear back from regulators as soon as the end of this month. If molnupiravir gets approved, it'll be the first pill-based therapy for COVID-19 that is proven to reduce the risk of developing the severe form of the disease, as defined by life-threatening cases requiring hospitalization. That's huge, and it might spell yet another way to transition out of the current public health crisis.

It'll also make Merck plenty of money. By the end of 2022, management estimates that sales of molnupiravir could total as much as $7 billion. While $7 billion isn't a massive amount in comparison to Merck's trailing-12-month revenue of $52.6 billion, it's likely to at least catalyze a moderate amount of growth in the company's share price.

3. Vaxart

Unlike the projects from Merck and Pfizer, Vaxart's (VXRT -3.16%) pill isn't a therapy for COVID; it's an oral vaccine.

Its candidate has a few game-changing advantages which could make it into a strong seller globally. Because it's a pill rather than a jab, it doesn't require healthcare workers to use supplies like sterile wipes, syringes, or examination gloves. Nor does it require people to experience the lingering pain of getting a jab. It could be administered with minimal hands-on labor from healthcare workers -- or it could be mailed directly to recipients, reducing the labor burden to near zero. Most importantly, the tablet would be shelf-stable, which would simplify the logistics of delivering doses, and enable the vaccine to be sold in areas with low levels of economic development.

All of that is exciting, but investors will need to wait for quite sometime before the biotech even has a chance of turning its innovation into profits. Vaxart's phase 2 trials for the pill should be done in the first quarter of 2022, with the results reported shortly thereafter. Beyond that, the company currently has no medicines that are approved for sale, nor any product that's remotely close to being approved.

Vaxart's fortunes are riding on its vaccine. For investors comfortable with risk, Vaxart's pill could look like a massive winner, but the company isn't for the faint of heart.