It might seem like everything is going well for COVID-19 vaccines right now. The first Americans have already been vaccinated with Pfizer's (PFE -0.11%) and BioNTech's (BNTX -0.47%) BNT162b2. Moderna (MRNA -1.56%) could win U.S. Emergency Use Authorization (EUA) in a matter of days.

But there have been some setbacks for other coronavirus vaccine makers. AstraZeneca (AZN 1.20%) and Sanofi (SNY 1.45%), in particular, have hit bumps in the road with their COVID-19 vaccine programs. The bad news for these big drugmakers, though, could be great news for Pfizer and Moderna. Here's why.

Gloved hands holding two vaccine vials labeled COVID-19.

Image source: Getty Images.

Behind the bad news

In some respects, AstraZeneca's news wasn't all that bad. The company reported an average interim efficacy of 70% for COVID-19 vaccine candidate AZD1222 in November. That's above the 50% minimum efficacy threshold set by the Food and Drug Administration. It's also in line with the efficacy levels achieved by vaccines for other viral diseases. There were two problems, though.

AstraZeneca calculated its average efficacy by combining two groups of participants. One group initially received a full dose of AZD1222 followed by another full dose at least one month later. The efficacy of this regimen was only 62%. That's well below the 94% and 95% levels reported by Moderna and Pfizer, respectively.

However, AstraZeneca did have another group that achieved an efficacy of 90% by taking a half dose of AZD1222 followed by a full dose. So what's the problem? The company didn't include this dosing regimen in its U.S. late-stage study. 

Sanofi and its partner, GlaxoSmithKline (GSK 0.19%), lag behind these other COVID-19 vaccine makers. And now they'll trail even further. Last week, the two drugmakers announced a delay in their coronavirus vaccine program because interim results from a phase 1/2 study indicated a low immune response in older adults. 

What happens now? Sanofi and GSK plan to develop the vaccine candidate with "an improved antigen formulation" that they hope will boost the immune response in older adults. Instead of potentially having the vaccine on the market by the middle of 2021, they're now shooting for late next year. 

Why Pfizer and Moderna could benefit

The U.S. government's Operation Warp Speed signed deals earlier this year to buy 300 million doses of AstraZeneca's COVID vaccine and 100 million doses of Sanofi's and GSK's vaccine. Those agreements only become effective, though, if the vaccines win an EUA.

To be sure, there's still a real possibility that both of these experimental vaccines will eventually secure an EUA. But the issues for AstraZeneca and Sanofi/GSK could increase the urgency for the U.S. to obtain additional doses of other vaccines to be able to fully vaccinate Americans.

The U.S. government has already upped its agreement with Moderna from 100 million doses to 200 million. There are reports that it's in talks with Pfizer about buying more doses after turning down an opportunity to do so earlier

The issue comes down to simple math. To vaccinate all Americans with these two-dose vaccines, the U.S. needs around 660 million doses. The current deals with Pfizer and Moderna meet less than half of that goal.

Johnson & Johnson could supply 100 million doses of its experimental COVID-19 vaccine if it proves to be both safe and effective. But there's no guarantee that will be the case at this point. The U.S. also has a deal with Novavax for 100 million doses of its coronavirus vaccine candidate. But the biotech hasn't even started its U.S. late-stage study yet.

Any way you look at it, the pressure is greater now than in the past for the U.S. and perhaps other countries to turn to Pfizer and Moderna for additional doses of their vaccines. Billions of more dollars just might be on the way for the two companies.

Opportunities for aggressive and conservative investors

My view is that the market hasn't totally priced in this added potential for Pfizer and Moderna. I also don't think that these stocks would be penalized much if AstraZeneca and Sanofi/GSK win an EUA next year.

This presents opportunities for both aggressive and conservative investors. Aggressive investors could like Moderna. The biotech stock has skyrocketed this year to a seemingly frothy valuation. But additional sales of its mRNA-1273 vaccine could give the shares even more room to run. Conservative investors should like Pfizer, which has other growth drivers and a solid dividend.

Everything has gone well for Pfizer's and Moderna's COVID-19 vaccine programs so far. And things just might get even better.