Novavax (NVAX 2.31%) is a beaten-down COVID stock that has seen its shares plummet 85% since the start of the year. Mounting losses and drastically slashed guidance, plus a COVID-19 vaccine market that looks to be diminishing in size, are the key reasons why investors have been bearish on the stock this year.

However, the company did receive good news recently. The Food and Drug Administration (FDA) granted its vaccine Emergency Use Authorization (EUA) as a booster for adults. And the Centers for Disease Control and Prevention (CDC) gave people 18 years of age and older the green light to use it as a booster, even if they've received Moderna or Pfizer shots as their primary doses.

It's a win for the company. But does this news make Novavax's stock a buy, or is it simply too little, too late?

Nearly half of eligible adults haven't received a booster yet

There's a significant opportunity for Novavax to reach a huge portion of the market. Data from the CDC suggests that close to half of people who have obtained both of their primary COVID-19 vaccine shots still haven't obtained a booster. And because the CDC has given the OK to mixing and matching, that means Novavax isn't limited to people who have obtained its vaccine.

There are some restrictions in place on the authorization, however. The FDA says the shot should be administered to people who aren't able to access an approved mRNA-based bivalent COVID-19 booster, or where the mRNA booster isn't "clinically appropriate" for them. But Novavax's booster can also be accessible to adults who simply choose to receive the shot, "because they would otherwise not receive a booster dose of a COVID-19 vaccine."

Novavax's COVID shot is a more traditional, protein-based vaccine, as opposed to the relatively new mRNA technology that vaccines from Pfizer and Moderna use. For people who prefer a more traditional shot or who had bad side effects from the mRNA vaccines, Novavax could be a welcome alternative for their boosters. But gauging just how much demand this represents in light of the restrictions is difficult if not impossible.

Earlier this year, Novavax obtained an EUA for its vaccine as a primary two-dose series for people who haven't yet been vaccinated. With 68% of the U.S. population fully vaccinated, there is still room for Novavax's shots to be used as primary doses. But it ultimately comes back to the same question as boosters -- whether individuals who haven't received doses are waiting for a traditional vaccine like the one from Novavax or if there are other reasons holding them back.

Novavax can compete on price

Although demand for vaccines and boosters may diminish amid a return to normal in the economy, Novavax could potentially make its vaccine more popular by offering a lower price than its rivals now that the market is changing. 

Next year it will be the private markets, rather than the government, that dictate the demand for COVID-19 vaccines and boosters. The government is running out of its supply of COVID-19 vaccines, and a lack of funding will mean that it won't be stocking up on them anymore.

While that could negatively impact demand, prices are going up for vaccines. Pfizer is reportedly planning to sell its vaccine at up to $130 per dose. That's more than four times the $30 per dose that the U.S. government has been paying thus far.

For Novavax, this creates an opportunity for the company to potentially undercut its rival to wrestle away some market share. 

Does this news make Novavax a buy?

Novavax has incurred losses totaling $1.5 billion over the trailing 12 months, and its business is heavily reliant on its COVID vaccine for revenue right now. As a result, there simply haven't been many reasons to be bullish on the stock of late.

This recent news does improve the prospects for the healthcare company but it will still come down to how many people end up taking Novavax's vaccine. At this point, there's still uncertainty as to whether people who haven't received boosters or primary doses have been waiting for Novavax's shot or if they're holding out for other reasons. 

Until there's more clarity around that, this will remain an ultra-risky stock to buy. The news for Novavax is great, but it still needs to translate into sales. And because that's by no means a guarantee, the best option for investors is to simply hang tight and wait and see if that happens before buying shares of Novavax.