What happened

Food and Drug Administration (FDA) authorization for a product typically delivers a nice stock price boost for the affected company. This, however, wasn't the case with vaccine specialist Novavax (NVAX -0.47%) on Hump Day, as the latest FDA green light had the opposite effect, driving the shares down by almost 4% on the day.

So what

The FDA has granted emergency use authorization (EUA) for Novavax's booster coronavirus shot, an adjuvanted version of its NVX-CoV2373. There are significant caveats to this, however; the EUA covers the booster only for adult use, and for recipients for whom an mRNA bivalent booster vaccine is either unavailable, or inappropriate for their health status.

The two leading coronavirus jabs (and boosters) on the U.S. market utilize mRNA technology -- Spikevax from biotech Moderna, and Comirnaty developed by Pfizer and BioNTech.

Compounding the fact that there are fairly strict limits on the administration of Novavax's booster, the general take-up of the latest coronavirus boosters in this country has been relatively slack. Many Americans are averse to COVID-19 vaccines in the first place, while many primary series recipients are weary of the pandemic and hopeful that it is fading.

"According to CDC data, almost 50% of adults who received their primary series have yet to receive their first booster dose. Offering another vaccine choice may help increase Covid booster vaccination rates for these adults," Novavax quoted its CEO Stanley Erck as saying.

Now what

While Novavax offers a novel coronavirus vaccine on the U.S. market, as NVX-CoV2373 is protein-based, the company still hasn't shaken its reputation as a Johnny-come-lately in the Great Covid Jab Race. It was the fourth and last developer to have its vaccine either approved or authorized by the FDA, and this rather limited authorization for its booster isn't going to help matters.