If you think that you missed out on the coronavirus vaccine furor in the market last year, think again. Even though Pfizer and Moderna have already successfully commercialized their coronavirus jabs, demand for vaccination is still far outstripping supply. For the foreseeable future, there's plenty of vaccine market share to go around.

The three companies I'll discuss today are still working on their coronavirus vaccine candidates, and they probably won't be finished anytime in the first half of the year. Investing in them is risky, as they aren't profitable and they have no recurring revenue from sales yet. However, they were excellent stocks to own in 2020, thanks to their participation in the vaccine race, and there are several signs that 2021 could be favorable for investors too. So let's dive in.

A vial labeled COVID-19 Vaccine is balanced on top of a syringe, with a stock chart in the background.

Image source: Getty Images.

1. Vaxart

If you had a choice, would you get vaccinated against the coronavirus by getting an injection, or by taking a pill? For me, it's a no-brainer to pick the pill. Vaxart (NASDAQ:VXRT) is working on making such a pill, and that's one of the reasons that it rocketed by more than 1,100% over the last 12 months. Sometime this quarter, the company expects to have data from its coronavirus candidate's phase 1 clinical trial, and it plans to start phase 2 shortly thereafter.

If its vaccine gets regulatory approval, it'll have a few advantages over competitors. Vaxart's pills can be stored at room temperature, and they don't need a healthcare worker to administer. With fewer barriers for healthcare systems to purchase and deploy its product, it will have a market niche in underdeveloped areas. More importantly, Vaxart's oral delivery system could be used to vaccinate people against other diseases too. Even if its coronavirus program is running a bit late, the utility of Vaxart's pill-formulation technology will likely enrich its investors down the line.

2. Arcturus Therapeutics Holdings

Arcturus Therapeutics Holdings (NASDAQ:ARCT) was a little-known mRNA medicine company before its stock's run-up of 578% over the last year. With its potentially single-dose candidate still in progress, it plans to proceed with the final phase of clinical trials in the second quarter. This means that the company could get an emergency use authorization (EUA) from regulators sometime in the latter half of the year. There's just one problem: It might not be as effective as competing products. Early analysis of clinical trial data suggests that the candidate might only be 62% effective. The approved vaccines from Pfizer and Moderna both boast efficacy upwards of 90%.

Still, Arcturus hasn't finalized its dosing regimen, which it will do before it initiates phase 3 trials. It's possible that it could see a more competitive level of efficacy if it increased the size of its single doses, or experimented with a multiple-dose regimen. If investors buy the stock now, they could see it grow if the efficacy issue is cleanly resolved. But at its current valuation, it's unlikely that Arcturus will expand as much as it did during the initial months of vaccine hype.

VXRT Chart
Data source: YCharts.

3. Inovio Pharmaceuticals

Inovio Pharmaceuticals' (NASDAQ:INO) 176% expansion since the start of last year is nothing to sneeze at, but it could still have significant upside. The company's coronavirus candidate is in phase 2 clinical trials, though it's just one of 15 pipeline projects aiming to prevent or treat other infectious diseases and cancers. If you're interested in investing for the long term, each of these other projects offers a chance for the stock to grow. Still, investors should be aware that biotech companies are quite risky to buy before they have any products on the market, no matter how many promising projects they may have in the works.

Then there's Inovio's vaccine injector device, the Cellectra. While it may not be as convenient or painless as taking a pill, the Cellectra has attracted attention and a $71 million investment from the U.S. Department of Defense (DOD) to speed its development and manufacturing. If the company succeeds in making a useful injector that can be used to rapidly administer any other vaccine, it'll be a strong catalyst for long-term growth. Until then, there's plenty of time to buy the stock before its coronavirus trials approach their conclusion.