What happened

Meme stock investors had a satisfying Monday, with three of the top names in that rather loosely defined group -- AMC Entertainment (AMC -3.73%), GameStop (GME -4.41%), and Tonix Pharmaceuticals (TNXP -3.16%) -- all convincingly beating the S&P 500 index's gain.

The trio closed the day higher by, respectively, 6.9%, 3.5%, and 4.2%.

A man and a woman with a fan of cash.

Image source: Getty Images.

So what

Stock bulls were running rampant on Monday, largely because of the very happy news that the coronavirus vaccine developed by Pfizer and BioNTech received full FDA approval.

Previously, the jab -- now brand-named Comirnaty on our shores -- had only been granted Emergency Use Authorization, an important distinction.

Now what

The impact of the vaccine's approval on Tonix Pharmaceuticals is clear. The biotech company is developing its own coronavirus vaccine, and the FDA's nod on Pfizer's proves the regulator is eager to get jabs through the pipeline and into human arms.

It also affects AMC and GameStop, but in a less direct way: Some holdouts might get their shots now that there's a fully FDA-approved vaccine. That's potentially good news for venues potentially packed with humanity, like AMC's movie theaters.

The reasoning is similar for GameStop. Outside of console or hot game launch days, the company's many brick-and-mortar locations aren't usually packed with people, but with greater inoculation rates and a lower risk of infection, more people are likely to visit the stores.