What happened

Shares of Vaxxinity (VAXX -8.27%) were up 36.8% this week as of Thursday's close. The stock closed last week at $1.74. Vaxxinity's shares opened on Monday at $1.70 and then soared on Thursday to $3.95 before dropping a bit to $2.38 by Thursday's close. The stock has a 52-week low of $1.26 and a 52-week high of $11.10. The stock is still down more than 57% this year.

So what

Vaxxinity is a clinical-stage biotech that focuses on vaccines to treat chronic diseases. The company didn't report any news, so this is likely a "sympathetic" play, so called when another company with a similar drug reports potentially positive news. In this case, the other companies were Eisai and Biogen, which reported on Wednesday that their therapy lecanemab, in its phase 3 study, slowed clinical decline for Alzheimer's patients on a scale that measures cognitive and function, compared with a placebo. 

It may be a case of a rising tide raising all ships, or at least companies that have an Alzheimer's therapy in the works. Vaxxinity, for its part, has a therapy, UB-311, that is in a phase 2 trial to treat Alzheimer's and has a Food and Drug Administration Fast Track designation. It also has UB-312 in a phase 1 trial to treat Parkinson's disease and Lewy body dementia. 

Now what

The run-up was a bit much, which explains why it collapsed a bit later in the day. The study by Eisai and Biogen will have to be scrutinized for exactly how effective it was. On top of that, there's no guarantee that the success for lecanemab will help any of Vaxxinity's Alzheimer's or dementia therapy candidates. Bear in mind too that Vaxxinity reported it didn't earn any revenue in the third quarter and lost $19.3 million.