Shares of Novavax (NVAX) dropped from their highs after Andrew Left's Citron Research predicted the shares will fall to $15.

The firm, known for shorting the names it writes about, tweeted:

"As much as Citron wants a vaccine $NVAX is a serial promise and non deliver on every virus. Insiders sold most holding 85% lower last year. Bal sheet upside down and $$ is needed for NanoFlu. Expect secondary soon and stock back to $15. Retail mania!!"

Shares of Novavax, which hit as high as $26.34 today, are now up 21%, or $4.09, to $23.26.