When you think of coronavirus vaccines using messenger RNA (mRNA), you probably think Pfizer and Moderna. The two companies burst into the forefront with mRNA technology last year, and since then, they've vaccinated more than 103 million and 69 million Americans, respectively.

But Pfizer and Moderna may not be the only players in the world of mRNA coronavirus vaccines for very long. Superstar-investor Cathie Wood has her eye on a much smaller player that aims to apply for emergency use authorization in Vietnam this year. In fact, the founder and CEO of Ark Invest recently bought shares in this biotech company.

Now the question is: Should you follow Wood and scoop up shares of this underdog? Let's take a look.

A patient takes a selfie while getting vaccinated.

Image source: Getty Images.

One-dose mRNA vaccine

Arcturus Therapeutics (ARCT -2.56%) isn't a newcomer to the vaccine race. Last year, the biotech dazzled investors with the possibility of a one-shot mRNA vaccine. Like Pfizer and Moderna, Arcturus uses mRNA to give the body's cells instructions to produce a copy of the coronavirus spike protein, which is the protein the virus uses to infect. The body then produces antibodies to block infection.

But Arcturus' technology is slightly different. It uses self-amplifying mRNA, so the original strand of mRNA expands in the body's cells. As a result, a greater amount of protein is expressed.

The advantage of this technology is that a company can dose its vaccine much lower. And that results in savings when it comes to manufacturing.

Arcturus shares soared more than 1,000% from the start of 2020 through early December.

ARCT Chart

ARCT data by YCharts.

But since then, they've fallen more than 60% from their December high. The reason? In a phase 1/2 clinical trial, Arcturus' vaccine candidate ARCT-021 produced lower neutralizing antibody levels than the Moderna and Pfizer vaccines.

Neutralizing antibodies are seen as key since their role is to block infection. Investors worried the Arcturus candidate may not be able to compete with the high efficacy of the Moderna and Pfizer vaccines.

What's changed since that point? Arcturus has put the focus on another vaccine candidate, ARCT-154. This next-generation candidate targets variants of concern.

The company's phase 2 and phase 3a trial segments are ongoing, and it recently launched dosing in the phase 3b part of the trial. Arcturus is conducting phase 3b in Vietnam -- and plans to request marketing authorization in December. The company says its candidate has "the potential to become a best-in-class option for Vietnam and many other countries around the world."

Improving immune response

ARCT-154 is different from ARCT-021. Arcturus has worked on its technology to improve stability and immune response. In non-human primate studies, ARCT-154 spurred neutralizing antibody levels that were 14.4-fold to 25.9-fold higher than those of ARCT-021. So Arcturus' next-generation candidate may have an easier time competing with rivals when it comes to efficacy.

Arcturus' clinical studies are testing ARCT-154 as a primary series, as well as for use as a booster following vaccination with the Pfizer vaccine. If results are positive, Arcturus could be on its way to revenue.

Right now, only 17% of Vietnam's population is fully vaccinated, so there's likely room for a latecomer in this market. Eventually, if Arcturus' data on using its shot as a post-Pfizer booster is compelling, it could represent further opportunity.

Now you may be wondering: What happened to ARCT-021? Arcturus continues to advance the candidate through clinical trials. In fact, a global entity is funding a phase 3 study of the potential product. True, neutralizing antibody levels have been lower than those produced by Pfizer and Moderna, but ARCT-021 maintains the advantage of potentially being a one-shot vaccine.

Last year, Israel and Singapore signed supply agreements with Arcturus for ARCT-021. If Arcturus succeeds with the phase 3 trial, this could mean revenue is on the horizon.

Should you follow Cathie Wood?

Does this mean you should follow Cathie Wood into what may become the next mRNA success story? Arcturus' situation is looking better now than it did earlier this year. ARCT-154 and even ARCT-021 could play a role in coronavirus prevention post-pandemic. Experts say the virus will stick around -- and the world will continue to need vaccines.

But Arcturus remains risky right now. Failure can happen at any stage -- even in phase 3 trials. And the neutralizing antibody levels in the earlier ARCT-021 trial remain a concern. It's important to note Arcturus only has three other programs in the pipeline, and two of those are preclinical. If the COVID-19 vaccine programs fail, revenue is far off.

If you're a cautious investor, you're better off watching this stock from the sidelines. But if you're an aggressive investor and want to bet on the next batch of COVID-19 stocks, you may consider following Cathie Wood. And that means taking a closer look at Arcturus and possibly picking up a few shares.