What happened

Shares of Novavax (NVAX 3.69%) are sinking 13.8% this week as of the market close Thursday, based on data from S&P Global Market Intelligence. This decline came even though Novavax didn't make any new announcements in recent days.

Perhaps the most likely reason for the stock continuing to drop relates to news from Pfizer (PFE -0.11%) and BioNTech (BNTX 0.31%). The two partners announced on Tuesday the initiation of a clinical study evaluating a version of their COVID-19 vaccine targeting the coronavirus omicron variant.

A healthcare professional giving a vaccine shot to a person.

Image source: Getty Images.

So what

Investors appear to be worried that the opportunities for Novavax's COVID vaccine could be significantly reduced if an omicron-specific vaccine enters the market. Pfizer and BioNTech definitely have a big head start over their rivals. Pfizer CEO Albert Bourla has stated that an omicron vaccine could be ready as soon as March.

Moderna (MRNA 2.81%) is well ahead of Novavax on this front as well. The company advanced its omicron-specific vaccine into phase 2 testing this week. 

But in December, Novavax announced encouraging immune responses for its COVID vaccine against the omicron variant. The company is also developing its own omicron-specific vaccine.

Now what 

It's possible that positive catalysts for the vaccine stock could be on the way. Novavax expects to file for Emergency Use Authorization for its NVX-CoV2373 within the next few days. The company could also begin to recognize sales of its vaccines in other countries.