What happened

Shares of several top COVID-19 vaccine makers were sinking on Tuesday. Pfizer (PFE 0.55%) stock was down 2.7% as of 11:09 a.m. EDT. Shares of Pfizer's partner, BioNTech (BNTX 0.58%), were falling 7%. Moderna (MRNA 1.69%) stock was tumbling 5.4%. Novavax (NVAX 3.54%) was the biggest loser with its shares declining 8.1%.

Why did these vaccine stocks slump? It wasn't because of any bad news related to COVID-19 vaccines. None of the companies issued press releases that would explain the declines. Instead, we're probably just seeing downward pressure on prices as investors take some profits off the table after a nice jump for each of the stocks on Monday following the U.S. Food and Drug Administration full approval of the Pfizer-BioNTech vaccine.

A healthcare professional giving a shot in the arm of a patient.

Image source: Getty Images.

So what

It's really not all that surprising that these stocks would give up much of the gains from Monday. FDA approval for the Pfizer-BioNTech vaccine was fully expected.

Also, the approval doesn't impact Pfizer or BioNTech financially over the short term. The U.S. had already ordered 500 million doses of the companies' COVID-19 vaccine, Comirnaty, plus another 500 million doses to donate to other countries.

If Pfizer and BioNTech didn't receive any near-term material benefits from the full FDA approval, the other vaccine makers certainly didn't either. Moderna hasn't won full FDA approval of its COVID-19 vaccine yet, although it's practically a slam dunk that the approval will be on the way. Novavax hasn't even submitted for U.S. Emergency Use Authorization of its COVID-19 vaccine candidate yet.

Now what

Pfizer, BioNTech, and Moderna hope to win EUAs for their vaccines in younger children within the next few months. The companies also will pursue full FDA approvals in these age groups. Novavax plans to file for EUA of its COVID-19 vaccine in the fourth quarter, with submissions in the U.K. and Europe coming even sooner.

Perhaps the most important thing to watch with all of these stocks is the supply deals they secure for 2022 and beyond. All four companies have already signed some supply agreements for delivery beginning next year.