Novavax's updated COVID vaccine is here. What to know about the shot.

About 4 million Americans got updated COVID vaccines in September, according to the U.S. Department of Health and Human Services. Now, another vaccine option has arrived.

What’s happening?

On Oct. 3, the Food and Drug Administration (FDA) authorized the updated COVID-19 vaccine by Novavax for people ages 12 and older. The Centers for Disease Control and Prevention and its advisory panel had already recommended the vaccine before the FDA authorization, so Novavax has all the regulatory approval it needs to start distributing vaccines — meaning Americans now have three brands of COVID shots to choose from this fall.

How is the Novavax vaccine different?

Side effects in clinical trials were similar to side effects experienced with other COVID vaccines, including headache, nausea, muscle or joint pain, injection site tenderness, and pain and fatigue.

But unlike the Pfizer and Moderna vaccines, which use first-of-their-kind mRNA technology to deliver immunity, the Novavax vaccine utilizes a protein-based approach.

Emily Smith, an assistant professor at the George Washington University Milken Institute School of Public Health, explains that while mRNA vaccines tell your body to create a protein that your body then responds to and triggers immunity, the more “traditional” protein-based vaccine platform provides the protein itself. She tells Yahoo Life that the updated Novavax vaccine can be a good alternative for those hesitant to use the newer mRNA approach.

“I think many people are excited about it because it doesn't feel as new of a technology, so they just feel more comfortable or confident with it,” Smith says. “This is kind of a more traditional approach to getting immunity. One isn't better or worse than the other, I don't think — just a different approach to having your body respond.”

Like the updated Pfizer and Moderna vaccines, the new Novavax vaccine targets the XBB strains of the virus, meaning it should offer protection against dominant strains circulating nationwide.

“All three vaccines have shown good protection against COVID-19,” Bethany DiPrete, an assistant professor of epidemiology at the University of North Carolina, tells Yahoo Life. “With this new approval, Americans now have even more options for the type of vaccine they can receive.”

Who can get the Novavax vaccine?

The Novavax shot is approved for anyone over age 12. (Children 6 months and up can get the Moderna or Pfizer vaccines instead.)

CBS News reports that Novavax was previously authorized only as a first booster dose for people unwilling or unable to get an mRNA shot. But now, DiPrete explains that if you’ve previously been vaccinated with other COVID vaccine brands, you can get a single dose of the new Novavax vaccine if it’s been at least two months since your last COVID shot. If you’ve never received a COVID shot, you’ll get two doses of the new Novavax shot spaced three weeks apart.

When will it be available?

"I would expect that the whole process would allow us to start seeing shots in arms taking place next week," Novavax chief commercial officer John Trizzino told Yahoo Finance, adding that "vaccinations are going to continue to take place over the next eight weeks.”

Novavax says that the shots will soon be available nationwide at thousands of locations, including doctors’ offices, clinics and pharmacies. Free shots will also be available through the Vaccines for Children and Bridge Access Program, according to USA Today.

So far, the rollout of Moderna's and Pfizer’s mRNA vaccines has been rocky. Some people have encountered canceled appointments or have been unable to get a vaccine appointment at all, in part thanks to reported shipping delays and insurance issues stemming from the end of the COVID public health emergency earlier this year.

Trizzino told Yahoo Finance that the extra-cold storage requirements for mRNA vaccines are an added complication that the protein-based Novavax vaccines shouldn’t encounter.

"[The mRNA doses are] shipped frozen, and the distributors are thawing and relabeling prior to shipping. And it's our understanding that that's created a backlog," he said. "We've already arranged where there are situations where a particular facility within that distributor is dedicating to do that process, we're [avoiding] that facility and making sure that we're being fulfilled out of another warehouse."