We're still fighting COVID-19, and as we approach winter the number of infections and hospitalizations might increase. Of course the best thing to do is to vaccinate. We know that COVID is mutating, like the flu, but at a much slower rate than the flu. 

According to the Centers for Disease Control and Prevention (CDC), the delta variant is by far the most common COVID variant, making up 99% of new cases. And of course the vaccines were developed to stop the original strain of the coronavirus. Will the vaccines work against delta? And what stocks should we buy to "immunize" our ports? Our trio of Fools suggest you might want to take a jab of Novavax (NASDAQ:NVAX)Pfizer (NYSE:PFE) and Eli Lilly (NYSE:LLY).

Doctor injects a vaccine into a tiny globe.

Image source: Getty Images.

1. Novavax will boost your returns  

It's a great time to be a Novavax investor. The biotech recently submitted its COVID-19 vaccine candidate to the World Health Organization (WHO) for an emergency use listing (EUL). Assuming its vaccine is authorized, Novavax will start distributing over a billion doses of its vaccine in India and the developing world. I'm expecting the stock to zoom higher once emergency use is authorized.

Most of the world is still not vaccinated, and so the Novavax vaccine will be a great relief. Investors can look forward to a cascade of emergency authorizations around the world, including in the U.K., Australia, Canada, Japan, South Korea, the E.U. and the U.S.  

Of course, in many countries a majority of the population have been vaccinated already. In the U.S., 77% of adults have had at least one shot, according to the CDC. Nonetheless, as we head into 2022, demand for booster shots will probably escalate because of the delta variant. And the trial data suggests that Novavax's vaccine will be strong in that regard.

Last month the company released data from a phase 2 trial in Australia that found a booster shot of its vaccine caused six times as many antibodies against the delta variant than the first round of shots. And while the Novavax vaccine has similar efficacy rates to the mRNA vaccines -- all three vaccines target the spike protein -- some observers have noted that Novavax's candidate is actually safer than the vaccines currently on the market.

This may make the vaccine a prime candidate for booster shots. mRNA vaccines have a tendency to cause stronger side effects with additional doses. This is perhaps why the FDA allowed for a booster dose of the Pfizer vaccine, but only for certain populations. With a cleaner safety profile, Novavax might snag a larger percentage of the booster market as we head into 2022.

2. Pfizer: A proven vaccine innovator

George Budwell: The novel coronavirus is probably here to stay. Despite a global effort to tamp down the pandemic through social distancing, travel restrictions, and widespread vaccination programs, most virologists and epidemiologists alike are convinced that the virus will morph into a chronic seasonal illness. At Roche's (OTC:RHHBY) recent research and development day, for example, the company's medical team estimated that COVID-19 will likely become an endemic respiratory illness, with roughly 200 million to 500 million new infections per year.

The main reason is the virus's ability to mutate into more transmissible forms such as delta and its offshoots. That means that vaccine developers will have to keep churning out modified versions of their vaccines to stave off future outbreaks.

Which company has the best shot at meeting this demand? For my money, I think Pfizer and its partner BioNTech (NASDAQ:BNTX) have what it takes. The pair are already trialing delta-specific versions of their potent messenger RNA vaccine. This updated vaccine reportedly entered clinical trials last month.

The vaccine works by targeting the full spike protein of the delta variant. Assuming this modified version of the vaccine works, it could be on the market as soon as the first quarter of 2022. In addition, the dynamic duo are also evaluating the efficacy of booster shots of the original vaccine against delta and related variants.

Now, Pfizer and BioNTech aren't the only companies pursuing a delta-specific variant vaccine. But they have proven to be among the best at tackling this troublesome public health problem. So, if you're hunting for a company that can generate sustainable vaccine sales from COVID-19, Pfizer should be at the top of your list. 

3. The best COVID data this side of vaccines

Patrick Bafuma (Eli Lilly): You want to talk about a company that has made a difference with the delta variant? Look no further than mammoth pharma Eli Lilly.

Its JAK inhibitor Olumiant for COVID-19 has been quite a patient success story. The powerful anti-inflammatory medication approved for emergency use authorization in both children and adults with COVID-19 is one of the few treatments this side of steroids that has been shown to reduce mortality in hospitalized patients with severe disease.

In fact, for patients on bi-pap or high-flow oxygen (essentially on the brink of being put on a ventilator), mortality with Olumiant in one trial was 17.5%, compared to 29.4% for patients who did not receive the Lilly treatment. It also reduced mortality for patients requiring a ventilator, which has eluded many treatments thus far. Even better, the frequency of adverse events, serious infections, and blood clots were similar between the two treatment arms.

Olumiant is actually much cheaper than other COVID-19 treatments, with the list price for a two-week course of Olumiant ringing in at just under $1200. This compares favorably to approximately $2500 to $3000 for Gilead's (NASDAQ:GILD) remdesivir, and over $2200 a dose for Roche's Actemra. For patients hospitalized due to breathing problems from this coronavirus, Olumiant is taking on the delta variant. It currently is shaping up to be a cornerstone of inpatient therapy and without added harm.

Considering that Roche's Actemra experienced a sales boost in 2020 of around $800 million due to COVID-19-related treatment, I estimate that Olumiant could produce another $100 million to $150 million in revenue per quarter while COVID-19 is still terrorizing the U.S. While that is a blip on the map considering Lilly raked in $6.7 billion in revenue in the last quarter alone, we're looking at delta fighters here, and Olumiant is just that. Plus, Lilly has a lot more going for it.

Despite its massive $220 billion-plus market cap, the pharmaceutical powerhouse is still growing revenue 12% year over year excluding COVID-19 antibody revenue (23% including COVID-19 treatments), with 79.3% non-GAAP gross margins. Its diverse portfolio in oncology, diabetes, and immunology insulates the mega-cap from any potential economic downturn, as patients will still need diabetes and cancer treatment.

Its pipeline is looking rather plump as well, with the 2019 buyout of Loxo Oncology ready to pay dividends. The company could launch at least two new indications or line extensions per year for the next three-plus years. Management is shareholder-friendly too, authorizing a $5 billion share repurchase program this past May.

With a 1.5% dividend yield, steadily growing revenue, a handful of potential blockbusters in the works, and shareholder-friendly management -- not to mention Olumiant holding the best data yet for COVID-19 treatment not named vaccine -- Eli Lilly can help fend off any delta-induced damage, be it to your health or your portfolio.

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.