What happened

Shares of Inovio Pharmaceuticals (INO 2.81%) were slipping 5.7% lower as of 2:58 p.m. EDT on Tuesday. The biotech didn't make any announcements that would cause its stock to slide. Instead, we're seeing a continuation of a sell-off that began in July.

So what

It's more important to understand why Inovio's shares have been falling for several weeks than it is to delve into one day's movement. The bottom line for Inovio is that confidence about the prospects for its coronavirus vaccine candidate, INO-4800, has decreased.

Scientist with vaccine bottle and syringe

Image source: Getty Images.

But didn't the company announce positive results from a phase 1 study for INO-4800 in late June? Yes. The problem is that the details from that study haven't yet been released. Some investors are likely wondering if the actual data was as good as Inovio indicated.

Another issue is that Inovio still hasn't received a green light to begin a phase 2/3 study of its COVID-19 vaccine candidate. The company had said that it expected to initiate the study this summer, but summer will soon end.

Now what

Inovio could easily reverse its slide by getting a Food and Drug Administration go-ahead for its phase 2/3 study of INO-4800. It could also reassure investors with solid (and detailed) data from the phase 1 study of its vaccine candidate. In the meantime, the biotech stock is likely to remain highly volatile.