The coronavirus pandemic in the U.S. is now in its third wave. For stock investors, it's important to have at least one stock in your portfolio that can perform well amid the pandemic. Whether that's a business that does testing, is working on a vaccine, or provides a treatment option for COVID-19, a good coronavirus stock can help generate some returns for the foreseeable future, while other investments may struggle during these challenging times. It's also a great way to diversify your portfolio.

Two options are Gilead Sciences (NASDAQ:GILD) and Abbott Laboratories (NYSE:ABT). Gilead is well-known for its drug remdesivir, which can help treat patients with COVID-19, while Abbott has been a major player in testing for the virus. Let's take a close look at these two companies to see which one is the better coronavirus stock to buy today.

Gilead: Remdesivir approval hasn't ended its slump

Shares of Gilead are down 10% year to date, well below the S&P 500, despite the 2% the stock gained in July following an analysis of positive trial results. That's also in spite of great news on Oct. 22, when the U.S. Food and Drug Administration (FDA) approved remdesivir for treating patients with COVID-19; if they're 12 or older and require hospitalization, they'll be eligible to use the drug.

This is a significant milestone, as remdesivir is the first drug the FDA has approved for use in treating COVID-19. Until recently, remdesivir had only been used under an emergency use authorization (EUA), which the FDA first issued in May. Under an EUA, the FDA may permit health officials to use an unproven drug during a public-health emergency like COVID-19. But the formal approval indicates that remdesivir has passed the agency's full vetting process.

A young woman on a bus wearing a surgical mask and looking at a phone

Image source: Getty Images.

However, despite the exciting news, shares of Gilead continued to fall. While remdesivir has a good safety profile, there are still questions about its efficacy. A recent report in the New England Journal of Medicine found that while remdesivir did help patients recover from COVID-19 faster than a placebo, the mortality rate at the 15-day mark was still 6.7%, even for patients on the drug. That compared to a mortality rate of 11.9% using a placebo.

Remdesivir has been used for months to treat patients with COVID-19, but it's not helping their outcomes as much as was hoped. This is the likely reason many investors aren't as bullish on this stock as they once were. When the FDA granted remdesivir an EUA on May 1, there was still lots of optimism surrounding the stock and it was trading at close to $80 a share. At the end of October, however, it closed at just $58.15.

On Oct. 28, the California-based company released its earnings for the third quarter, which ended Sept. 30. Revenue of $6.6 billion was 17% higher than in the prior-year period, thanks in large part to sales of remdesivir. Excluding those, the company's product sales were only up 2% year over year. The total growth for the segment was 18% when including the COVID-19 drug.

These were good results for Gilead, but they may not be sustainable -- not with vaccines on the way and more treatment options available, such as the Regeneron antibody cocktail (REGN-COV-2) that President Donald Trump took in October. Moderna and Pfizer may also release phase 3 trial results this month for their COVID-19 vaccines candidates.

While remdesivir has strengthened Gilead's numbers of late, that may prove to be a short-term trend.

Abbott: Lower sales growth, but demand for testing continues

Another option to consider is Abbott, which is becoming a big name in COVID-19 testing. As of Aug. 14, the company said it had shipped 7 million rapid ID NOW tests, 6 million molecular lab tests, and 13 million antibody tests related to COVID-19. And that doesn't include the numbers from BinaxNOW, a new antigen test which received an EUA from the FDA on Aug. 26; it costs just $5 and produces results in 15 minutes. Then, on Oct. 12, the FDA also granted an EUA for Abbott's AdviseDx serology test, which can help determine whether someone was recently infected with COVID-19.

On Oct. 21, the Illinois-based company released its results for the third quarter of 2020, which ended Sept. 30. It reported worldwide sales of $8.9 billion, for 9.6% growth year over year. The key reason for the growth was, unsurprisingly, a boost from its testing and diagnostics segment, which generated year-over-year sales growth of 38.2%, climbing to $2.6 billion in quarterly revenue. Over the past nine months, the company's total sales have gone up just 1.3%; that figure would be a lot worse if not for diagnostic sales rising more than 14% during that time.

The company is optimistic that demand for testing will still be strong in 2021, even if there's a vaccine, particularly when it comes to testing for antibodies and determining whether someone was previously infected with the novel coronavirus.

Abbott updated its guidance for 2020, with management now expecting diluted earnings from its continuing operations to come in at $2.35 per share or better. That's up from the $2 it had forecast in the previous quarter.

Which is the better overall buy today?

Here's a quick look at how both of these healthcare stocks are doing this year:

GILD Chart

GILD data by YCharts.

Abbott's stock has been outperforming Gilead's thus far, and that trend is likely to continue, because demand for treatments like remdesivir will inevitably decline as vaccines become available. Testing, however, will be necessary as long as the pandemic continues, to ensure that people are able to go back to work and that other activities can begin to return to normal.

Even once a vaccine bcomes available, there's no guarantee that everyone who gets it will be protected, or that it will remain effective against the virus indefinitely. That's why Abbott's rapid tests will continue to be in strong demand.

And given remdesivir's uninspiring results, there's little reason to be optimistic that suddenly, after months of using it, healthcare providers will uncover a way to make it more effective in treating patients. Without strong incentives to use remdesivir, demand for the drug could falter, especially since there are other options available, and a five-day treatment of remdesivir will cost many patients more than $3,000.

Abbott's the more likely company to continue strong sales amid the pandemic. That makes it the better coronavirus stock to buy today.

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.