What happened

Shares of Novavax (NVAX -4.21%) were trading 9.9% lower as of 11:52 a.m. EDT on Thursday. The company didn't announce any news, so why was its stock falling? There are three likely factors.

First, Moderna (MRNA -0.98%) reported disappointing third-quarter results before the market opened. That appears to be weighing on vaccine stocks in general.

Second, Novavax is scheduled to provide its third-quarter update after the market closes Thursday. Investors could be anxious about what management has to say.

Third, a law firm announced that it's "investigating claims on behalf of investors of Novavax" related to concerns about the possibility that the company's management engaged in securities fraud or broke the law in other ways. 

A healthcare professional giving a shot to a person.

Image source: Getty Images.

So what

Moderna posted lower-than-expected Q3 sales. It also cut its full-year revenue guidance. The issue was that the company hasn't been able to produce and ship as many doses of its COVID-19 vaccine as it initially expected.

These problems don't really relate to Novavax. However, it's possible that some traders are worried that it too could face manufacturing issues. Moderna's news may have reinforced those concerns.

As for Novavax's looming third-quarter update, there's really no way to know whether or not the company will announce anything that's unsettling. Actually, its management team should have a positive message considering that it has delivered thus far on the most recent timeline for completing regulatory filings for its COVID-19 vaccine, NVX-CoV2373.

The investigation launched by the law firm appears to be a fishing expedition at this point. No formal allegations of impropriety have been made against Novavax or any of its officers or directors.

Now what

We'll soon find out if Novavax's Q3 update gives investors reason for concern. Probably the most important thing to listen for will be the company's progress on filing for an Emergency Use Authorization (EUA) with U.S. regulators for NVX-CoV2373. Novavax confirmed on Wednesday that it remains on track to complete that EUA submission by the end of this year.