It's been a volatile year for Inovio Pharmaceuticals (NASDAQ:INO). In June, shares of the biotech company hit a peak, up over 800% since January; this has been one of the hot coronavirus stocks to buy this year. But in recent months it's been falling in value, and now it could make for an appealing investment to buy on the dip. Year to date, it's still up more than 260%, leaving the S&P 500 and its 8% returns in the dust.

However, with Inovio recently announcing that it will need to pause the trials for its COVID-19 vaccine candidate, investors are spooked. Let's take a closer look at what's happened with the company this year, why its stock is falling, and whether this latest setback is a reason to stay away from Inovio -- or if it's still an attractive buy.

It's been a roller-coaster ride for Inovio investors this year

Inovio is one of the companies working on a vaccine for COVID-19, and that has generated a lot of hype around its stock this year. The company uses its handheld smart device, Cellectra, to administer its vaccine candidate, INO-4800. The device uses an electrical pulse to open up small pores for plasmids to enter a cell. The company says this gives it an advantage over other approaches involving DNA or mRNA. In June, when investors learned that the U.S. Department of Defense had provided Inovio with $71 million in funding to help manufacture Cellectra devices, the healthcare stock skyrocketed to a peak of $33.79.

People working in a lab.

Image source: Getty Images.

Unfortunately, the rise to the top was short-lived. Days later, the company would release interim phase 1 data for INO-4800 that failed to satisfy investors. Although the results were positive and the study didn't uncover any serious health concerns, many analysts found the data underwhelming and not as detailed as what they were hoping for.

Then, to make matters worse, the company released horrible-looking second-quarter results Aug. 10. For the three-month period ending June 30, Inovio reported a net loss of $129.2 million. But this loss looked worse than it really was -- a revaluation of derivative liabilities related to convertible bonds saddled the company with $97.8 million in expenses. There was some good news, too, as Inovio updated investors on its phase 1 trials for INO-4800, which now showed that all 38 participants in the study "demonstrated overall immunological responses."

But the company hasn't been able to proceed with phase 2/3 trials of the vaccine, as it first needs to answer questions from the U.S. Food and Drug Administration (FDA) has about the company's vaccine and about Cellectra. Investors should know sometime in November whether the trials can continue; Inovio expects to respond to the FDA before the end of October, at which point the agency will notify the company of its decision within 30 days.

What does Inovio have in its pipeline besides INO-4800?

Including INO-4800, Inovio has a dozen products in its pipeline, but the only one currently in phase 3 is VGX-3100, which is a vaccine for the human papillomavirus (HPV). Currently, two late-stage studies are underway evaluating its effectiveness in treating HPV-related precancerous cervical dysplasia. The company expects that before the end of the year, it will have top-line results available from one of the studies. Management also expects to have full data available from its phase 2 trials evaluating the vaccine on patients with anal and vulvar dysplasia in the fourth quarter. According to a report from EvaluatePharma, VGX-3100 could generate annual sales of $622 million by 2024.

In addition to HPV, Inovio is also working on vaccines for Zika, Ebola, Lassa fever, MERS, and HIV, with the latter two the only ones that have made it to phase 2.

Is Inovio stock a buy?

By the end of 2020, Inovio will see readouts of its clinical studies and likely receive approval (or denial) of the continuation of its clinical trials. That means the roller-coaster ride this stock has given investors this year isn't coming to an end anytime soon. And while there are other drugs in the company's pipeline, all eyes will be on INO-4800 and the COVID-19 trials (if approved). With many vaccine companies already working on phase 3 trials, Inovio will be in danger of falling further behind them if it's unable to resume its trials this year. And without a COVID-19 vaccine, shares of Inovio could come crashing down.

With many questions surrounding the company's future, Inovio isn't an investment for the faint of heart. Investors are better off waiting until there's some clarity about whether Inovio can resume its trials for INO-4800. You may sacrifice some returns by doing so if the news is good, but you can also avoid significant losses if it isn't.

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.