On Saturday, February 27, the United States Food and Drug Administration granted an emergency use authorization for a third COVID-19 vaccine for people 18 and over.

This one is created by Janssen, the pharmaceutical arm of Johnson & Johnson. And it's not just another vaccine.

It has a few differences that are worth learning more about. In clinical trials, the Janssen vaccine appeared to be about 66% effective at preventing moderate-to-severe or critical cases of COVID-19 one month after injection. This easily clears the 50% mark [that] the FDA said it would need to see to green light a vaccine for emergency use.

There were also no deaths observed among people who got the vaccine. Now, you might know that the 66% figure is lower than the 90%+ effectiveness that previous vaccines have reported for the same time period, one from Moderna and one from BioNTech-Pfizer. However, it's worth noting that these numbers can't really be compared one-to-one.

The trials were set up in different places at different times and just not designed to line up with one another in that way. Plus, you have to remember that 66% effective doesn't mean that 34% of the people who received it still got sick. Instead, that number refers to 66% fewer people getting sick in the trial arm of the clinical trials compared to the placebo.

We have a whole episode planned on that, so keep an eye out. This vaccine also works a bit differently than the ones that have previously been authorized. Those use a genetic message encoded in a molecule called mRNA to persuade the human body to make bits of the virus, in particular, the spike protein [that] the virus uses to get into and infect cells.

That then teaches our immune system to recognize the spike if the real virus ever shows up. The Janssen vaccine also shows our body how to make the spike protein, although it delivers it in a different way. Instead of delivering mRNA, this vaccine packages the spike protein instructions as bits of DNA encased in a lab-made shell based on a virus.

This is called a "viral vector," and they've been used as a laboratory tool since the 70s. Now viruses are great at delivering genetic material, it's what they do so it makes sense to adapt them for our own use. The viral shell being used isn't from the virus that causes COVID-19, it's from another type of virus called an adenovirus.

In this case, the vector has been designed so it can enter cells but can't replicate. The virus in this vaccine can't cause an infection nor can the DNA it's carrying do anything to mess with your DNA. We already have other vaccines that work this way.

In the end, both these vaccine platforms accomplish the same goal: our cells end up making copies of the spike protein which alerts the immune system. That doesn't mean that this vaccine is exactly like the others in practice and there are a few differences that could be pretty useful. First of all, it's important to note that even if this were just another one to throw on the pile that would still be a good thing.

More vaccines being made means more shots into more arms. But DNA is also more stable than RNA. The viral carrier also helps protect the genetic material in the vaccine.

That means the Janssen Vaccine can be kept in the fridge for up to three months at 2 to 8 degrees Celcius. The mRNA vaccines, on the other hand, need to be kept super cold. This new vaccine was also tested and authorized as a single-dose vaccine.

Meanwhile, the BioNTeach-Pfizer and Moderna vaccines were authorized based on clinical trials where two doses were given. This combined with the ease of shipping and storing means that the Janssen vaccine might be easier to distribute to more remote places. The Janssen trials were also conducted after the appearance of a few new variants of the virus that causes COVID-19.

These variants have mutations that affect the spike protein and some evidence is emerging that some of them could make the virus more contagious or help it escape vaccines. But the Janssen trial was conducted at times and in places where some of these new variants were circulating, like South Africa and Brazil. And the vaccine still protected people.

This is great because the Moderna and BioNTech-Pfizer vaccines were tested before these variants emerged and some data suggest that they might not be as effective against some of them. Though pretty much everyone is working on boosters to address the variants, including Janssen. Finally, and this is really cool, some limited data suggest the Janssen vaccine may help prevent asymptomatic infection roughly a month after injection, with efficacy of around 74%.

The FDA says to interpret this cautiously, but this could be really helpful if it turns out to be true. Most of the vaccine clinical trials have set prevention of more severe disease as the main goal. Both are good endpoints, but if the vaccine stops asymptomatic infections, it should also stop disease transmission.

See it's actually possible that our vaccines might simply tamp down the infection without stopping it entirely. If that's the case, they'd just keep you from getting super sick. That is still a win since fewer people getting seriously ill would mean things like more open hospital beds, but it would mean you might still be contagious.

On the other hand, if the vaccine halts all infection then we're really in business. The virus would have nowhere to go. There's also some evidence that the BioNTech-Pfizer and Moderna vaccines halt transmission, and if that's true, the more the merrier.

Johnson and Johnson say they're expected to have 20 million doses out the door by the end of March and that's 20 million doses closer to getting this thing under of control. Science success stories like this one always get my curiosity following and that's a great opportunity to learn something new over at Brilliant. Because if all these biotech companies can make a vaccine in a year then maybe I can finally learn calculus!

And Brilliant will help you the whole way along with a series of interactive courses from the basic to the more advanced. There are plenty of other courses in the store as well if you hop over and check them out you can save 20% on an annual premium subscription at brilliant.org/scishow.