The late Sen. Everett Dirksen from Illinois was credited with saying, "A billion here, a billion there, and pretty soon you're talking real money." Whether or not he actually said those exact words, Dirksen would probably agree that Pfizer (NYSE:PFE) and Moderna (NASDAQ:MRNA) are swimming in real money these days thanks to their COVID-19 vaccines.

Pfizer expects that the COVID-19 vaccine that it markets with partner BioNTech will generate sales of around $26 billion this year. Based on its advance purchase agreements in place as of March 31, Moderna anticipates that its COVID-19 vaccine will rake in sales of more than $19 billion. 

It's quite possible, though, that both of those sales projections could be way too pessimistic. Here's why Pfizer and Moderna could soon be big winners in a new $22 billion market.

Gloved hands holding a syringe with needle next to a coronavirus vaccine vial with an Indian flag in the background.

Image source: Getty Images.

A big barrier removed in a big market 

Neither Pfizer nor Moderna has made any sales of their respective COVID-19 vaccines in India thus far. That could be about to change.

In the past, the Indian government demanded that companies conduct clinical studies of their COVID-19 vaccines in India before they could win authorization. This was a requirement that Pfizer and Moderna didn't like. In February, Pfizer even withdrew its application for emergency use authorization in the country. 

Now, however, the Drugs Controller General of India has removed the requirement for an in-country clinical study. This decision only applies, though, to COVID-19 vaccines that have already been approved for restricted use in the U.S. or other countries included on the World Health Organization's Emergency Use Listing. 

This waiver appears to be especially great news for both Pfizer and Moderna. The two companies had requested that the Indian government allow them to secure authorization without the need for local clinical studies. 

Pfizer's and Moderna's $22 billion-plus opportunity

While the U.S. has largely turned the corner in the fight against COVID-19, it's a much different picture in India. The country continues to reel from a large number of COVID-19 cases. Low vaccination rates are a big part of the problem. Only 3.3% of India's residents are currently fully vaccinated.

Just how big is the opportunity in India for Pfizer and Moderna? The country has a total population of close to 1.39 billion. So far, around 228 million doses of COVID-19 vaccines have been given. That means roughly 1.16 billion people in the large country have yet to receive a vaccine.

Of course, some of those individuals are children in age ranges for which Pfizer's and Moderna's vaccines haven't yet been authorized in other countries. If we assume that around 65% of the total unvaccinated population could receive a COVID-19 vaccine, that gives us a total market size for Pfizer and Moderna of around 750 million.

What we don't know for sure is how much the drugmakers will charge for their vaccines in a developing nation like India. The low end of Moderna's price range has been $25 per dose, although the U.S. paid less because it helped fund the development of the company's vaccine. Pfizer charged $19.50 per dose to the U.S. government and around $18.60 per dose to the European Union. 

Perhaps Pfizer and Moderna will charge less per dose to the Indian government. Even at $15 per dose, though, the potential COVID-19 vaccine market opportunity for the two companies tops $22 billion. At the low end of the price charged in the U.S. and Europe, the Indian market would represent an opportunity of nearly $28 billion. 

A few remaining hurdles

Don't start counting all of those extra dollars for Pfizer and Moderna just yet, though. There are still a few hurdles the companies must jump, even assuming they win authorization in India.

First, Pfizer and Moderna won't be the only players in the Indian COVID-19 vaccine market. AstraZeneca, Bharat Biotech, and Russia's Gamaleya Research Institute of Epidemiology and Microbiology have all received emergency authorizations for their respective vaccines in India. 

Second, there's no guarantee that the majority of Indians will want to receive COVID-19 vaccines. There are reports of significant vaccine hesitancy in the country. 

Third, it's possible that Pfizer's and Moderna's vaccines will prove to be ineffective at providing protection against the Delta variant that's prevalent in India. So far, both vaccines have fared pretty well against emerging coronavirus variants. However, a recent study found that Pfizer's COVID-19 vaccine produces lower levels of neutralizing antibodies against the Delta variant discovered in India. 

Even with these hurdles, though, Pfizer and Moderna could have a major opportunity to boost sales assuming their vaccines become available soon in India. Their vaccines could be more effective than others at providing protection against the Delta variant. The two companies also have their act together with respect to production more than most other rivals.

Investors don't seem to be factoring this sizable market potential into the valuations of either stock. Pfizer's shares currently trade at a little over 11 times expected earnings. Perhaps surprisingly, Moderna is even cheaper, with the biotech stock trading at a little over 10 times expected earnings. Success in India just might present a solid catalyst for both stocks.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.