Pfizer's top-selling product in 2019 and 2020 was Prevnar 13, a pneumococcal vaccine. In both years, it generated sales of over $5.8billion. This is a huge amount of money for a product that has been very successful.Prevnar 13 has fallen from the top of Pfizer's most-sold products. Pfizer and BioNTech (NASDAQ :BNTX) developed the COVID-19 vaccine BNT162b2, which generated $7.8 billion in sales during the first half 2021. Pfizer estimates that the vaccine will bring in $33.5 billion for the year. Pfizer will make around $17 billion this year from BNT162b2 despite BioNTech splitting its profits.There could be more money in the future. Pfizer is currently working on its next COVID-19 blockbuster, but it's not a vaccine.Stopping the coronavirus from spreadingPfizer has said for some time that it would not limit its efforts to combat COVID-19 to vaccines. The company has been working on potential treatments for the infectious diseases. Last week, the company gave an update on a promising treatment in its second quarter conference call.The class of antiviral drugs known as protease inhibitors has been proven to be effective in HIV and hepatitis C treatment.In March 2013, Pfizer began an early-stage clinical trial to evaluate oral protease inhibitor, PF-732133232. In its Q2 update, Pfizer had positive news from the study.Mikael Dolsten, chief scientific officer, stated that PF-07321332 was more effective than expected to inhibit coronavirus virus replication in phase 1. Dolsten stated that experimental protease inhibitors showed strong antiviral activity in preclinical tests and could be effective against all known COVID-19 variants.The safety profile of the antiviral drug is good so far. Dolsten stated that doses up to 500 mg per day were safe over a 10-day span.Pfizer promoted the oral protease inhibitor to phase 2/3 testing in July based on these encouraging results. For individuals who have had close contact with someone suffering from COVID-19, the company will test PF-07321332 for 5-day and 10-day treatments.A big market opportunityPfizer believes that there could be a market of hundreds of millions of patients for its protease inhibitor. This is not surprising considering the rapid spread COVID-19 exposure from the delta variant.The U.S. Food and Drug Administration has granted an Emergency Use Authorization (EUA), to Regeneron's (NASDAQ.REGN) antibody mixture REGEN-COV for treatment of COVID-19 hospitalized patients and post-exposure prophylaxis. Regeneron's therapy has its limitations.First, REGEN COV is very expensive. It costs more than $2,000 per dosing. It must be administered subcutaneously or infusionally. The current U.S. EUA is only applicable to persons who have been exposed to COVID-19, who are at high risk for developing COVID-19, and have not been fully vaccinated.Pfizer's oral PF-0732133232 is much more convenient than REGEN COV. The big drugmaker has not yet revealed the pricing of the antiviral treatment, but it could be cheaper if EUA approval is granted. This would open up new markets for people who are less likely to get exposed to COVID-19.Soon?Pfizer's next COVID-19-related blockbuster should not take too long. If the testing in phase 2/3 goes well, Pfizer believes it will be able file for U.S. EUA within the fourth quarter.Albert Bourla, CEO of Pfizer, stated in Q2 that he has given permission to produce "significant quantities" (or oral protease inhibitors) of the drug so that large quantities of doses can be made if EUA is granted. He said that Pfizer will accept the risk in making this investment as it is "the right thing to do."The Pfizer-BioNTech COVID-19 vaccination will be a bigger catalyst than PF-07321332. Pfizer will not have to split the profits from the oral therapy like it did with BNT162b2. Pfizer is very likely to produce another blockbuster in 2022 if the COVID-19 drug's late-stage testing proves successful.
