We've known for a while that the COVID-19 vaccine developed by Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) was highly effective in individuals ages 16 and up. The two partners recently announced an impressive 100% efficacy for the vaccine in children between the ages of 12 and 15. In this Motley Fool Live video recorded on March 31, Motley Fool contributors Keith Speights and Brian Orelli discuss why neither of these stocks soared after the news about this great efficacy in kids.

Keith Speights: Pfizer and BioNTech announced results from their phase 3 study and this study showed 100% efficacy for their COVID vaccine, BNT162b2. Kids ages 12 through 15. So the companies plan to move pretty quickly to file for Emergency Use Authorization.

So last I looked, I'm going to check really quick here, Brian. So BioNTech stock is up around 5%. It's actually up just a little under 5% right now. Pfizer stock is up all of 0.4%. At one point this morning, it was even down a little bit.

Brian, I'm sure investors might be wondering, with this great news, why do you think these two stocks didn't jump even more?

Brian Orelli: It makes sense that BioNTech would move more than Pfizer because it's a lot smaller, so it's a lot more dependent on this one vaccine. It's literally the company's only drug at this point, although some of their valuation is built on their pipeline. Potentially it's already priced in.

We already knew that the vaccine achieved at least 95% efficacy in adults and so there's a good chance it we'll be higher in kids as they have stronger immune reactions. In fact, they also looked at antibody levels and the antibody levels were higher in the kids than they were in the adults.

The other thing is we don't really know whether it's 100%. So they're only 2,260 kids in the study. So there's probably not that many kids in the placebo group. I scanned the press release a couple of times and I didn't see an actual number that they gave, but the placebo group presumably only had a few COVID-19 cases and so we're comparing that to obviously zero in the vaccine group.

But we're comparing zero to a small number, which I mean technically is 100%. But who knows, if they enrolled tens of thousands of patients like they did with the adults, whether we would get one or two cases in the vaccine group and then it's not 100 percent it's 90-something.

Then finally, I have heard some doctors argue that the side effects, however low for the vaccine, might actually be worse than just letting kids get COVID-19, at least for the average kid, and certainly sicker kids are going to want to get the vaccine because they're more likely to die. But the average kid is probably not going to die from COVID-19 and so the vaccination rates in this age group might not actually be all that high.

Speights: Yeah. I think that last point probably might be the biggest reason why these stocks didn't move as much. I think maybe some investors are just expecting that vaccination rates in kids won't be nearly as high and so this won't be as big of a boost for revenue as it might otherwise seem to be.

I don't know about kids between 12 to 15 years old. I haven't seen any census data on that specific age group. But I know that kids under 18 in the U.S. make up over 20% of the population. If vaccination rates were high, then this news could be very, very good for both of these stocks because it could really boost sales. I think you're right though. I mean, I think we will just have to see whether or not parents want their kids to be vaccinated.

Orelli: Part of it is going to be how prevalent COVID-19 is in a few months or whatever, when kids are eventually eligible to get the vaccine. So if it's fairly low, I think that vaccination rates are going to be fairly low. If it's still pretty high, I think there's going to be a big push by doctors even to get the vaccines to kids because they are, while they are not going to die from it, they're going to be transmitters of it until we get them vaccinated.

Now we're going to have less unvaccinated people get COVID-19. Adults that are unvaccinated get COVID-19 who may actually die from it. So I think there's an advantage to getting it, but only if it's the prevalence of COVID-19 is at a decent level.

Speights: Right. Pfizer's CEO mentioned that they hope to win EUA pretty quickly so that they could start to vaccinate this age group before the start of the next school year, which will be here and I guess school isn't wrapped up yet for this school year, but the summer will pass quickly. Do you think there is even a possibility some schools will require or heavily push for their students to be vaccinated before they return to school in the fall?

Orelli: Yeah. I don't know. I have no idea. I think if they did there may be a lot of pushback. I don't know. We'll have to wait and see. I guess there's some pushback, even on the more common kids vaccine so will have to wait and see, I guess.

Speights: My hunch is that you're right. My hunch is that there will be considerable pushback, even though the vaccine does appear to be safe and effective for kids. But we'll see. But neither of these stocks, well, I guess BioNTech stock did move a little bit, but that's not unusual for smaller biotech stocks to jump 5%.

Orelli: I mean, if you probably look at BioNTech, you can find some 5% moves on no news.

Speights: Yeah. Their CEO can sneeze and the stock moves 4 or 5%, right? We'll see what happens on this story.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.