What happened

Shares of several top COVID-19 vaccine developers were soaring this week. Novavax (NVAX -7.42%) was the biggest winner. The stock was jumping 16.9% for the week as of the market close on Thursday, according to data from S&P Global Market Intelligence. Shares of BioNTech (BNTX -1.05%) were up 9.8% for the week. Moderna (MRNA -0.15%) stock was rising 9.4%. 

There was one common denominator behind the gains for these vaccine stocks: concerns about the Omicron variant. Omicron caused record daily cases of COVID-19 in the United Kingdom. Health officials in the country called the Omicron variant the "most significant threat" since the beginning of the pandemic. The strain continues to spread in the U.S. and elsewhere. 

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

Image source: Getty Images.

However, each of these three companies has also benefited from other news this week. Novavax announced regulatory submissions for its COVID-19 vaccine in Japan and the United Arab Emirates. Data was revealed in recent days showing that boosters of Moderna's vaccine and the Pfizer-BioNTech vaccine provided protection against the Omicron variant. Moderna also won regulatory approval in Japan for booster shots.

So what

It makes sense that Novavax is the top performer of the group in recent days. For one thing, Novavax's shares had fallen the most from their highs coming into the week. The stock also had a higher short interest than BioNTech and Moderna. Positive news for more heavily shorted stocks tends to cause them to rise more as short-sellers cover their positions.

The gains for BioNTech and Moderna could be temporary, though. While the Omicron variant appears to be more contagious than previous coronavirus strains, vaccine makers won't benefit unless countries order additional doses as a result. That hasn't happened so far.

Moderna's booster approval in Japan wasn't a surprise. The country's regulatory agency had already approved the Pfizer-BioNTech booster. 

Now what

The key things for investors to watch with BioNTech and Moderna are the companies' supply deals for 2022 and beyond. The spread of the Omicron variant could lead to additional orders in the coming months. However, it's still too early to know for sure if that will be the case.

Meanwhile, Novavax has multiple potential catalysts coming up. The company expects to file for U.S. Emergency Use Authorization (EUA) of its COVID-19 vaccine by year end. Novavax also awaits regulatory decisions in several countries, including Australia, Canada, New Zealand, and the United Kingdom as well as key decisions from the European Union and the World Health Organization.