The coronavirus outbreak has been a major theme in the stock market these past few months. Investors bet on companies working on treatment and prevention, and some shares -- particularly those of clinical-stage biotech players -- skyrocketed.

Now the question is whether it's too late to invest in coronavirus stocks. Well, it depends on which ones. Here are three that make a great addition to your portfolio right now:

A researcher's gloved hand holds a syringe with coronavirus vaccine.

Image source: Getty Images.

1. Pfizer

If you want to bet on cutting-edge vaccine development but don't want the risk that comes with investing in a clinical-stage biotech company, you can opt for Pfizer (NYSE:PFE). The big pharma company partnered with BioNTech (NASDAQ:BNTX) to advance the German biotech company's investigational messenger RNA (mRNA) coronavirus vaccine program.

Last month, the partners said they began dosing the first participants in a phase 1/2 clinical trial in the U.S. and Germany. The dosing evaluation portion of the trial will include as many as 360 volunteers in the U.S. in two age groups. After initial safety and immune response data is available for the 18 to 55 group, the trial will immunize participants in the older set.

Pfizer and BioNTech have started human testing later than rivals such as Moderna (NASDAQ:MRNA) -- also working on an mRNA vaccine -- or Inovio Pharmaceuticals (NASDAQ:INO). But the partners are actually testing four vaccines simultaneously. That's an advantage, as it allows them more than one chance for a win. Each vaccine has a different combination of mRNA format and target antigen. The technology uses mRNA to deliver genetic information to cells so they can make proteins to prevent infection.

Pfizer's collaboration with BioNTech sounds promising, but what I like is that, even if the coronavirus program falters, Pfizer still makes a solid investment. Pfizer's biopharma business reported an 11% increase in first-quarter revenue, led by anticoagulant Eliquis and kidney cancer drug Inlyta. Pfizer shareholders should also benefit from the company's merger of its off-patent and generic business Upjohn with generic giant Mylan (NASDAQ:MYL). This will streamline Pfizer's business, paving the way for more growth. Pfizer investors, with 57% of the new company when the deal closes in the second half, also will benefit from dividends from that new entity.

2. Abbott Labs

The U.S. Food and Drug Administration (FDA) has granted Abbott Laboratories (NYSE:ABT) emergency use authorization for five coronavirus tests over the past few months. In May, Abbott landed a contract with the U.K. government to supply millions of its laboratory-based IgG antibody tests. These tests, by detecting a protein left behind late in the illness, indicate whether a person has had the coronavirus.

But all hasn't been rosy for Abbott. The company recently faced headwinds after a New York University study found its fastest coronavirus test resulted in too many false negatives. Abbott defended its test, saying the test detected 21 out of 23 cases in a study of 1,000 people in Washington. That means 91% sensitivity, or accuracy of positive results. And another study showed sensitivity of more than 94%. Abbott says various factors such as handling and storage impact test outcomes. This particular test, which involves use of a swab, is meant to be done near the patient.

Use of Abbott's coronavirus tests in the coming months should offer more evidence regarding their efficacy. While things look promising overall, I'm most optimistic about Abbott for its portfolio as a whole.

Medical devices are a particularly strong driver of growth. The company makes 38% of its revenue through that business. One of Abbott's star products is its FreeStyle Libre continuous glucose monitoring (CMG) system for diabetes care, which posted a sales gain of more than 60% in the first quarter. Regulatory clearance of the second-generation version -- Libre 2 -- is taking more time than some would like, but a potential nod from the FDA could be a positive catalyst for Abbott shares.

3. Novavax

I wrote about Novavax (NASDAQ:NVAX) last month, saying I was a bit hesitant about how it might afford its coronavirus vaccine program. A day after my article was published, Novavax announced that the Coalition for Epidemic Preparedness Innovations would invest as much as $384 million (after an earlier $4 million investment) in the company's work.

With the funding worry out of the way, the Novavax story has brightened for me. The company last month started enrolling the first patients in a phase 1/2 trial for its vaccine. The study will include about 130 volunteers who are between ages 18 and 59 in Australia. The second part of the study will take place in various countries, including the U.S.

Like the other companies I've recommended here, the coronavirus work looks good, but something else looks even better. Novavax recently reported positive phase 3 data for its flu vaccine. NanoFlu met all primary endpoints in the study, and the company will submit it for regulatory approval through the FDA's accelerated approval pathway. This would be Novavax's first commercialized product -- and in a significant market: The global flu vaccine market, at a compound annual growth rate of 7.7%, is expected to reach $7.34 billion by 2026, according to Fortune Business Insights.

Novavax shares have soared 116% so far this year, and though NanoFlu data is strong, it's best to wait for the FDA's decision before calling this a victory. And that's why I only recommend this biotech stock if you have several investment years ahead of you and have tolerance for risk.

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.