Pfizer (PFE -2.00%) hasn't been bashful about playing up the prospects for its coronavirus vaccine candidate, BNT162b2, co-developed with BioNTech (BNTX -3.95%). The company even predicted that it would be able to submit its investigational vaccine for regulatory review as early as October 2020. Few, if any, of Pfizer's rivals have been so publicly confident.

But Pfizer hasn't attempted to draw attention to everything it's doing on the COVID-19 vaccine front. On the contrary, the big drugmaker is making a stealthy move that could cement its position as the clear leader in the coronavirus vaccine race.

Gloved hands holding several bottles labeled "coronavirus vaccine."

Image source: Getty Images.

Enter candidate No. 5

Most of the companies developing coronavirus vaccines have only one candidate, but not so Pfizer and BioNTech. From the outset, the BNT162 program included four COVID-19 vaccine candidates based on messenger RNA (mRNA) technology. 

The two companies initially reported positive results from an early stage clinical study that highlighted BNT162b1. However, Pfizer and BioNTech ultimately chose another candidate, BNT162b2, to advance to pivotal phase 2/3 clinical testing.

Now a fifth candidate is about to step up to the plate. SVB Leerink analyst Daina Graybosch wrote to investors last Friday that Pfizer's executives confirmed plans to initiate a phase 1 clinical study evaluating yet another COVID-19 vaccine candidate that's being called BNT162b3.

Pfizer and BioNTech saw enough promise for the newest vaccine candidate in preclinical trials to warrant the investment in conducting an additional phase 1 study. The clinical trial is expected to begin later this month.

Why Pfizer's move is smart

There were no press releases about BNT162b3. Pfizer CEO Albert Bourla didn't give any interviews touting the new pipeline candidate. But it makes sense that the company didn't trumpet its decision to advance BNT162b3 to clinical testing. After all, Pfizer and BioNTech are counting on success for BNT162b2, and don't want to rob that program of its thunder.

At the same time, Pfizer's and BioNTech's move to advance BNT162b3 is a smart one. Why? SVB Leerink's Graybosch hit the nail on the head in her note to investors, stating that having "multiple shots-on-goal puts them in a good position for the long-term catch-up vaccination, revaccination, and/or pandemic stockpiling markets."

The first wave of COVID-19 vaccines that hit the market almost certainly won't be the endgame. In other contagious diseases, follow-up vaccines that proved to be more effective and/or safer than earlier vaccines have gained tremendous market share.

Pfizer and BioNTech don't want to merely be the first to market with a COVID-19 vaccine. They want to be leaders in the coronavirus vaccine market over the long run. If BNT162b3 delivers on its potential, it could help make this goal a reality. 

A waiting game

What's next? It's pretty much a waiting game. 

Pfizer has already enrolled 23,000 of its targeted 30,000 participants in the late-stage study of BNT162b2. The company still thinks it will have sufficient results to know in October whether or not the vaccine works.

There's always the possibility of a snag along the way, though. AstraZeneca revealed on Tuesday that the late-stage study of its COVID-19 vaccine candidate AZD1222 has been paused to evaluate safety data after a suspected serious adverse reaction in a participant in the U.K. Pfizer's coronavirus vaccine program hasn't had any serious safety issues yet, but it's also had fewer participants in its studies.

AstraZeneca's pause highlights another reason Pfizer and BioNTech are wise to quietly begin testing a fifth candidate. Even if BNT162b2 stumbles, it's possible that BNT162b3 won't. Pfizer's diversified approach could be one of the best reasons to bet on the big pharma stock in the coronavirus vaccine race.