What happened

Though the FDA recently gave emergency use authorization (EUA) to Moderna's (NASDAQ:MRNA) mRNA-1273 coronavirus vaccine, the company's stock was a big dud on Monday. This was likely due to some scary-sounding news regarding one patient who was administered the vaccine before Christmas.

So what

The New York Times reported on Friday that Dr. Hossein Sadrzadeh, a geriatric oncology fellow at Boston Medical Center, said he developed a severe allergic reaction just after receiving his initial jab of mRNA-1273's two-dose regimen.

Minutes after getting his shot, Sadrzadeh said he experienced dizziness and an increased heart rate. He was allowed to administer epinephrine to himself with an EpiPen, which he keeps on hand due to a severe shellfish allergy.

Gloved hand filling a syringe from a vial.

Image source: Getty Images.

Boston Medical Center said that after his self-treatment the doctor was "evaluated, treated, observed, and discharged." It added that on Friday, he was doing well.

Moderna's vaccine is only the second of two coronavirus vaccines to receive an EUA; the first was Pfizer (NYSE:PFE) and BioNTech's (NASDAQ:BNTX) BNT162b2. Moderna was granted its authorization on Dec. 18, six days after Pfizer and BioNTech received theirs.

Now what

No biotech investor wants to hear about a reaction like Sadrzadeh's to their vaccine or drug, especially mere days after its authorization by a regulator. We still don't know precisely how effective mRNA-1273 will prove to be in mass inoculations, but we should remember that occasional adverse reactions are not unusual for any vaccine or treatment. Moderna didn't deserve such a sell-off on this news.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.