Many people who are closely following developments in the COVID-19 pandemic are familiar with remdesivir. Gilead Sciences' (NASDAQ:GILD) investigational antiviral drug has been seen by many as a promising treatment option for the coronavirus. In February, Bruce Aylward of the World Health Organization said, "There is only one drug right now that we think may have real efficacy and that's remdesivir." However, hope for remdesivir's efficacy in the fight against COVID-19 may be fading.

On May 1, the Food and Drug Administration granted emergency use authorization for remdesivir to treat patients with severe COVID-19. And with more patients being treated with remdesivir, there's more data available to help gauge its effectiveness. But the latest results, although encouraging, may not be what investors hoped for when they invested in Gilead.

Remdesivir can help patients -- but the results aren't definitive

On June 1, Gilead released results from a phase 3 trial. The study involved patients with a moderate form of COVID-19 in which they're hospitalized but didn't require ventilators. Patients were either on five-day or 10-day treatment courses.

A person in a hospital bed

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In the case of a 10-day treatment course, the results weren't statistically significant enough to suggest remdesivir was effective. But in the five-day treatment course, the results showed that at day 11, patients taking remdesivir were 65% more likely to see a clinical improvement versus those receiving the standard of care. Another encouraging data point was that there were no deaths reported for patients who were on the five-day treatment course, while there were four deaths among patients receiving standard of care.

What's concerning, however, is that over the longer 10-day course, the results weren't statistically significant, and weren't as encouraging as the results from the five-day course. So while the study presented some positive findings, it also raised more questions, such as why remdesivir could potentially be less effective when taken over a longer period.

There were 191 people on the five-day treatment course, 193 on the 10-day treatment course, and 200 patients who received standard of care.

Studies thus far have been underwhelming

In previous studies, the results relating to remdesivir have been conflicting. One Chinese study saw no significant improvements for patients who were taking remdesivir. But with 158 patients taking remdesivir and just 79 in the control group, it wasn't a large study, and the company didn't believe there was enough enrollment to produce meaningful results.

The U.S. National Institutes of Health conducted a study involving 1,063 patients, and the results there were much more promising. The study showed that patients were recovering from COVID-19 four days quicker than with standard care. 

While the larger study was encouraging, it still showed a modest improvement at best, especially when looking at whether the drug can prevent death. The mortality rate of 7.1% was an improvement compared to the 11.9% mortality rate of patients not taking remdesivir, it didn't prove the drug could keep patients from dying.

Should investors be worried based on the results?

Shares of Gilead were down after the company released its latest remdesivir results. And there's good reason for that: There's a lot riding on remdesivir. A lot of the hype surrounding Gilead's stock's been driven by remdesivir. In late April, shares of Gilead soared back to their 52-week highs after the results from the larger study were made available.

Investors see a significant opportunity for a drug that can treat COVID-19, an illness that's infected more than 6 million people around the world. And if Gilead doesn't have a successful treatment option for patients, there may not be enough of a reason to invest in a company that saw revenue growth of just 1.5% in 2019. 

There is still hope that the company can deliver growth -- on December 19, Gilead submitted a new drug application for filgotinib, which treats people with rheumatoid arthritis.  But that growth will likely pale in comparison to the opportunities remdesivir could create for Gilead if health officials were to use the drug on a wide scale to treat COVID-19 patients. 

Unfortunately, it's hard to see that happening without more positive results. While there's still the potential that subsequent studies could show more positive results and give health officials more insight under which circumstances remdesivir works, at this point it's hard to be optimistic given the lackluster results that investors have seen to date. There is still the question of pricing for remdesivir and the company is donating nearly 1 million doses of the drug to U.S. hospitals.

Beyond COVID-19, Gilead is a healthy dividend stock

Gilead's remains a good dividend stock to own with a yield of 3.7%, which is above the average 2% that investors get from the typical S&P 500 stock, and it trades at a modest 19 times earnings. But investors looking for some more attractive growth prospects may have to look elsewhere. For now, results from remdesivir studies are just not strong enough to suggest that the Gilead is a good buy solely for its COVID-19 work. But the stock can still be suitable for investors who are looking for a healthcare stock to invest in that pays an above-average dividend yield.