Pfizer (PFE -2.09%) already is the leader in the coronavirus vaccine market. The big pharmaceutical company and partner BioNTech became the first to launch a vaccine. And that product now has fully vaccinated 49 million Americans. That's more than rivals Moderna and Johnson & Johnson. Pfizer recently forecast $15 billion in coronavirus vaccine revenue this year.

But Pfizer isn't stopping there. The company is now ready to conquer another massive coronavirus market. That move could give it ownership of the entire coronavirus space...and this dominance could be right around the corner.

A nurse visits a patient at home and holds up a bottle of pills.

Image source: Getty Images.

More and more people have been getting vaccinations. And so far, vaccines are doing their job. But for people who already have COVID-19, options are limited. The U.S. Food and Drug Administration has fully approved Gilead Sciences' Veklury (remdesivir) for hospitalized patients. And the FDA has authorized antibody treatments for mild-to-moderate illness in high-risk individuals.

A pill for COVID

What's missing from the list is a simple medication that anyone can use at the first signs of infection. And that's what Pfizer may have. Pfizer CEO Albert Bourla told CNBC this week that its investigational pill to treat COVID-19 could be ready for commercialization by the end of the year.

That means Pfizer potentially could generate sales from the product as of that time. And it means Pfizer would likely dominate not only the vaccine market -- but also the treatment one. So far, other companies haven't taken ownership of the treatment market.

Gilead and antibody makers such as Regeneron Pharmaceuticals (REGN 0.82%) have faced two big challenges: Their treatments aren't for all coronavirus patients. And they aren't at-home treatments. Even antibodies must be administered by infusion in a healthcare setting.

Pfizer's investigational protease inhibitor wouldn't face those issues. Potentially, a general practitioner could prescribe the product to patients showing early signs of illness. That represents a massive market. Since the start of the pandemic, there have been more than 148 million confirmed cases of COVID-19 worldwide.

Experts say the coronavirus will be around well into the future. Of course, vaccinations surely will reduce the number of cases. But they won't completely put an end to the virus. In some cases, vaccinated individuals still catch COVID-19. And some people can't get the vaccine for medical or other reasons. So, it's likely the treatment market will remain big -- especially for a pill to be taken at home.

What about revenue?

It's too early to say how much this could represent in terms of revenue for Pfizer. We don't know how much Pfizer would charge for the eventual product. But we can look to Roche's flu treatment Tamiflu as a general guide. In Tamiflu's most profitable year -- 2006 -- it brought in annual sales of more than $2 billion, data from EvaluatePharma show.

Now, the question is: What are the chances of Pfizer bringing its coronavirus treatment candidate to market? It's impossible to predict whether trials will be successful. But here's what we know so far. The candidate is a protease inhibitor. It acts by binding to a viral enzyme (a protease) and preventing viral replication.

This type of drug has been used for years against other viruses such as HIV and hepatitis C. In those cases, protease inhibitors have been safe and well-tolerated. So, it's reasonable to be optimistic about the potential safety of such a treatment for COVID-19. In March, Pfizer began a phase 1 trial to test the safety of its investigational coronavirus treatment in healthy adults.

At the same time, Pfizer also is preparing to help people who can't be helped by this potential early treatment. The company is testing a protease inhibitor as an infusion for hospitalized patients. That's in a phase 1b multi-dose trial.

What does all of this mean for investors?

Pfizer's rapid advancement into coronavirus treatment is great news. And what's even better is its work on a general treatment that most people could use as soon as they develop symptoms. This offers Pfizer a vast revenue opportunity. This plus its current position in the coronavirus vaccine market equals potential for total coronavirus market dominance. And that could translate into major revenue over several years.

Pfizer shares haven't been big movers in spite of this massive revenue potential. That's because the pharmaceutical company has many commercialized products and doesn't depend on the COVID-19 program alone.

But that's OK. Revenue from Pfizer's full portfolio of commercialized products is on the rise. The company forecasts revenue may climb as much as 47% this year. And the recent spinoff of its Upjohn business means that unit will no longer hamper growth. These factors -- along with possible COVID market dominance -- should push Pfizer shares higher over the long term.