Coming in No. 2 isn't the ideal outcome for sports teams or companies. Everyone prefers to rank first. However, Moderna (MRNA -2.21%) has become accustomed to taking second place.

Moderna lagged behind Pfizer (PFE -1.07%) and its partner BioNTech (BNTX -0.12%) in securing Emergency Use Authorization for its COVID-19 vaccine, and its sales have trailed behind its competitors' vaccine, as well. Moderna recently filed for full U.S. Food and Drug Administration (FDA) approval of its vaccine, but Pfizer and BioNTech already won full FDA approval for theirs.

It now looks like Moderna will come in second yet again. Here's why boosters for Moderna's COVID-19 vaccine might not be available as soon as those for Pfizer-BioNTech.

A healthcare professional holding a syringe with needle and a vaccine vial.

Image source: Getty Images.

Data problems

Stephen Hoge, Moderna's president, had told investors in August that booster shots were likely coming. He stated that, due in part to the rise of the delta variant, a third dose "will likely be necessary to keep us as safe as possible through the winter season in [the] Northern Hemisphere."

The Biden administration signaled its agreement with that view a few weeks later. On Aug. 18, the Department of Health and Human Services (HHS) issued a press release stating that preparations were underway for booster shots of messenger RNA (mRNA) vaccines to be made available to all Americans beginning the week of Sept. 20.

Moderna submitted initial data for its COVID-19 vaccine booster to the FDA on Sept. 1, 2021. Six days earlier, Pfizer and BioNTech initiated the filing of a supplemental Biologics License Application (BLA) for a booster dose of its vaccine.

But NBC News reported late last week that federal health officials think they'll need more time to review Moderna's booster application than initially expected. Why? A person familiar with the process said that the biotech's data was "found inadequate and needs strengthening."

Moderna's initial data came from an amendment to its phase 2 study of COVID-19 vaccine mRNA-1273. This amendment allowed interested participants in the study to receive a third 50 microgram dose six months following their second dose. The company stated that this third dose boosted levels of neutralizing antibodies significantly above the benchmark for its phase 3 study across all age groups.

A potentially bumpy path to boosters

No issues were reported with the booster data submitted by Pfizer and BioNTech. As a result, U.S. regulators still appear to be on track to finalize a decision on boosters for the Pfizer-BioNTech COVID-19 vaccine by Sept. 20. It could be several weeks later before a decision is made on a Moderna booster.

Despite the HHS statement in August about the plans for booster doses, there could potentially be a bumpy path -- even for Pfizer and BioNTech. The FDA must determine the safety and effectiveness of third doses for mRNA vaccines. Also, the Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) must recommend booster doses.

The FDA is moving forward with its process. An advisory committee is scheduled to review the Pfizer-BioNTech booster data on Sept. 17. However, there is some uncertainty as to whether or not ACIP will recommend booster doses. 

Currently authorized or approved vaccines remain highly effective at preventing severe COVID-19 and hospitalization. This could weigh more heavily in ACIP's decision than data that shows the vaccines' efficacy in preventing infection has declined.

What really matters for Moderna

It's quite possible that a delay in finalizing a decision on Moderna's booster might not matter very much, if at all. Even if the FDA and ACIP give a green light for a Pfizer-BioNTech booster weeks before Moderna's booster, there won't be any near-term financial repercussions for Moderna. The U.S. has already ordered more than enough doses to fully vaccinate all Americans, with third doses included.

What really matters for Moderna -- and for all of the top vaccine stocks -- is whether or not boosters will be needed on a recurring basis. With a top World Health Organization (WHO) official recently stating that the coronavirus that causes COVID-19 "is here to stay," it's looking increasingly likely that boosters will be needed over the longer term.