Gilead Sciences (GILD 1.23%) has been making waves of late. The company's antiviral drug, remdesivir, is currently perceived as the most promising potential treatment for COVID-19. As a result, Gilead's shares are up by 22% year to date, while the S&P 500 is down by 15% since the beginning of the year.

Gilead's good fortune will continue if remdesivir officially earns approval from health industry regulators, but if the potential COVID-19 drug fails to prove effective in clinical trials, the company's shares could plunge. With this backdrop in mind, is now a good time to buy shares of Gilead Sciences?

Early data on remdesivir is encouraging 

On Feb. 26, Gilead announced it would initiate two phase 3 clinical trials to investigate the efficacy of remdesivir as a potential treatment for COVID-19. The company said the studies would enroll about 1,000 patients in several Asian countries, including 600 patients with mild manifestations of COVID-19 and 400 with severe manifestations of the disease; patients would receive oral doses of remdesivir for five or 10 days.

Doctor giving a thumbs up.

Image Source: Getty Images.

While we don't have official results from these clinical trials yet, some excellent news for remdesivir was recently released. According to STAT, a website that focuses on news from the healthcare industry, in a sample of 125 COVID-19 patients treated with remdesivir, including 113 with severe cases of the disease, most of them recovered and were released from the hospital, while two died. 

While we can't draw any definitive conclusions from that experiment, the early data is an encouraging sign that remdesivir could be an effective treatment for COVID-19. 

What about the company's lineup?

And Gilead has a lot more going on than its attempt to find a treatment for COVID-19. The company boasts a strong lineup of drugs, with particular strength as a market leader for HIV medicines. Gilead's HIV treatment Biktarvy saw its sales soar by 300% year over year to $4.7 billion in 2019, and it will likely continue to be a significant growth driver. Biktarvy is the top prescribed HIV treatment in the U.S., and also occupies one of the top spots in Europe. The HIV treatment space still has room to grow in both these markets.

Gilead expects Biktarvy to "remain [a] preferred treatment option for the majority of patients through 2033." And another of Gilead's HIV treatments, Descovy, also has room to grow. The company estimates that about 40% to 45% of HIV pre-exposure prophylaxis (PrEP) patients will be on Descovy by year's end, compared with 27% at the end of 2019.

With the growth of its HIV product sales, Gilead is looking to offset the decline in sales for its chronic hepatitis C virus (HCV) products, which were down by about 21.6% year over year in 2019 to $2.9 billion. Gilead also has several promising pipeline candidates. First, there's filgotinib, a potential treatment for rheumatoid arthritis (RA) the company submitted to the U.S. Food and Drug Administration (FDA) for review in December of 2019.

While there are other RA medicines, Gilead has high hopes for filgotinib because, according to the company, it "has a compelling and differentiated clinical profile that we believe may uniquely address the significant unmet need for patients with RA." Also, thanks to a partnership with Galapagos NV (GLPG 1.59%), which allows Gilead Sciences to help itself to several of Galapagos's pipeline candidates, Gilead Sciences could have more exciting opportunities ahead.

Gilead Sciences remains cheap

Shares of Gilead Sciences have posted even more gains as news about the potential efficacy of remdesivir has spread. However, despite its rally since the beginning of the year, Gilead's stock remains pretty cheap. The company is currently trading at 13.2 times forward earnings, with a forward price-to-earnings-growth (PEG) ratio of just 0.3.  At this price -- and given Gilead Sciences' strong lineup and pipeline -- investors would do well to buy shares of the biotech company right now.