What happened

Shares of Moderna (MRNA -3.58%) were sinking 7.2% lower as of 12:03 p.m. EST on Wednesday. It marked the second consecutive day of declines for the stock this week.

One likely reason behind Moderna's pullback is the entrance of a new rival in the U.S. COVID-19 vaccine market -- Johnson & Johnson (JNJ 0.06%). The healthcare giant won Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) for its vaccine over the weekend. President Biden also announced on Tuesday that Merck (MRK 0.09%) is working with J&J to accelerate the production of its single-shot COVID-19 vaccine. 

Some investors could also be reacting to the results of a real-world study published this week. This study found that a single dose of COVID-19 vaccines developed by Pfizer (PFE -0.43%) and BioNTech (BNTX -4.08%) and by AstraZeneca (AZN 0.07%) and the University of Oxford reduced the risk of hospital admission in the elderly by more than 80%.

Gloved hand holding vaccine vial and syringe with scientists, a microscope, and a test tube rack in the background

Image source: Getty Images.

So what

Should investors be worried about all of this? No. Biotech stocks like Moderna that trade at premium valuations tend to be highly volatile. Any hint of seemingly bad news can cause shares to fall.

But the latest news really isn't bad for Moderna. Johnson & Johnson's EUA won't hurt Moderna's sales of its COVID-19 vaccine, mRNA-1273. The company already has major supply deals locked up.

That real-world study showing good results for the Pfizer/BioNTech and AstraZeneca/Oxford vaccines isn't worrisome for Moderna, either. Had Moderna's vaccine been included in the study, it's quite possible that mRNA-1273 would have achieved similar results.

Now what

One of the most important things to watch with Moderna over the near term is the emergence of new coronavirus variants. The biotech has developed a version of its vaccine that targets the B.1.351 variant first identified in South Africa. The National Institutes of Health plans to soon evaluate the vaccine candidate in an early-stage clinical study.