What happened

Novavax's (NVAX -0.43%) Nuvaxovid vaccine against COVID-19 continues to rack up regulatory victories, but you'd never know that from the stock's performance on Monday. It fell by 2%, more or less matching the slump of the S&P 500 index on the day, despite a highly encouraging development on the regulatory front for the company and its jab.

So what

That morning, Novavax announced that Nuvaxovid had been authorized by the Food and Drug Administration (FDA) for use in individuals aged 12 to 17. This expands the vaccine's emergency use authorization (EUA) to cover that demographic; originally, the shot received its EUA from the American regulator in mid-July.

In contrast to the vaccines that have been available on the U.S. market for quite some time, Nuvaxovid is a protein-based formulation, as opposed to one built on newer mRNA-based technology. The two leading vaccines in this country -- Spikevax from Moderna, and Comirnaty, developed by Pfizer and German biotech BioNTech -- are mRNA shots.

Now what

There are two major "buts" dampening the apparent Novavax victory.

The most significant is that, according to the latest data, the coronavirus still seems to be in retreat. In particular, the number of cases is in steep decline, falling by 19% over the past 14 days. The numbers of hospitalizations and deaths, while not tumbling as steeply, are also on the decline.

Secondly, an issue that continues to plague Novavax and its jab is that it is very much a latecomer. The FDA started authorizing coronavirus vaccines at the end of 2020, and even though the coronavirus has proven to be worryingly adaptable and robust, we (thankfully) seem to be past its peak.