It's been roughly three and a half months since the U.S. Food and Drug Administration (FDA) authorized boosters for the COVID-19 vaccine developed by Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) for certain groups. Around two and half months ago, the agency granted authorizations for boosters for Moderna's (NASDAQ:MRNA) and Johnson & Johnson's (NYSE:JNJ) vaccines, with limitations for which individuals could receive the Moderna booster. 

A little over two weeks ago, the FDA broadened its Emergency Use Authorization for the Pfizer-BioNTech and Moderna boosters to include all adults ages 18 and older. Overall, close to 42 million Americans have received booster shots. 

Which vaccine maker is winning the battle of the boosters so far? It's still early, but Moderna appears to be ahead in several respects. 

A healthcare professional holding a syringe with needle near a person's arm.

Image source: Getty Images.

Analyzing the data

More booster doses of the Pfizer-BioNTech vaccine have been given than have been administered for the Moderna and J&J boosters. Pfizer and BioNTech are clearly in the lead on this front.

Chart showing number of people with a booster dose in the U.S. by COVID-19 vaccine type.

Source: U.S. Centers for Disease Control and Prevention.

You'd expect that more people would have received the Pfizer-BioNTech booster. It's been available for many Americans (including those ages 65 and older) for a month longer than the other two vaccine types.

Also, many more individuals received the Pfizer-BioNTech vaccine initially than received the other two vaccines. A lot of those people chose to receive the booster of the same vaccine that they received for their primary series. The chart below shows how the different vaccines stack up against each other based on the fully vaccinated numbers.

Chart showing number of people fully vaccinated in the U.S. by COVID-19 vaccine series type.

Source: U.S. Centers for Disease Control and Prevention.

So why do I maintain that Moderna is the biggest winner with boosters so far and not Pfizer or BioNTech? There are three reasons.

First, from a financial standpoint, Moderna's 18 million booster doses made it more money than Pfizer or BioNTech made from their 23.3 million or so booster doses. Moderna doesn't have to split its profits as Pfizer and BioNTech do.

Second, Moderna is gaining more traction with boosters than Pfizer-BioNTech or J&J are. A little over 25% of the number of fully vaccinated individuals receiving the primary series of the Moderna vaccine have received Moderna boosters. The ratio is 21.3% for Pfizer-BioNTech. 

Third, with the FDA allowing mix-and-match boosters, more people appear to be switching from another vaccine to Moderna than they are to any other vaccine type. For those who initially received the J&J vaccine, 42.5% so far have gone with the Moderna booster versus 31.2% for a Pfizer-BioNTech booster and only 26.2% for a J&J booster. 

Why is Moderna winning?

We don't know for sure why Moderna seems to be gaining momentum. However, I have a theory for why it could be happening.

My hunch is that many Americans have heard that Moderna's efficacy against the delta variant is higher than the efficacy of the Pfizer-BioNTech and Johnson & Johnson vaccines. The initial efficacy of the single-shot J&J vaccine was well below its two messenger RNA vaccine rivals. And the efficacy of the Pfizer-BioNTech vaccine appears to have waned more than the Moderna vaccine has with the rise of the delta variant. 

I suspect that preliminary data showing that a mix-and-match combination of the Pfizer-BioNTech primary series and a Moderna booster provides a higher efficacy could also be making a difference to some extent. Singapore's minister of health even recently recommended that citizens in the country who initially received the Pfizer-BioNTech vaccine get the Moderna booster.

What really matters

Don't expect Moderna's relative outperformance in boosters to do much for the vaccine stock. Many investors aren't paying attention to the data. And the U.S. has already purchased enough doses from Moderna to meet the demand, including boosters.

What really matters for Moderna is how strong the longer-term demand will be for its COVID-19 vaccine. The company's efforts fighting the new omicron variant could play a key role in shaping that demand. But the most important factors will be whether or not annual vaccines are required to prevent COVID-19 and, if so, what price Moderna will be able to charge.

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.