Just days after Pfizer said its COVID vaccination was more than 90% effective, Moderna says it’s moving to a new phase of testing and analysis for its vaccine.

Marketplace’s Nancy Marshall-Genzer has the news. The following is an edited transcript of her conversation with “Marketplace Morning Report” host David Brancaccio.

Nancy Marshall-Genzer: You have to have a certain number of infections before you can determine if a vaccine is effective. In Moderna’s vaccine trial, half of the 30,000 participants got the vaccine. The other half got a placebo. Moderna says around 50 of the volunteers have now gotten COVID-19. So, now it will analyze how many of them received the vaccine versus the placebo.

David Brancaccio: And what kind of vaccine is this one?

Marshall-Genzer: It’s the same type Pfizer is making. They’re not like a typical vaccine, which involves injecting inactivated virus into a patient. The Pfizer and Moderna vaccines use messenger RNA. The vaccine prompts the body to produce COVID-19’s spike protein. A person’s immune system then learns to attack and destroy it.

Brancaccio: OK, so apparent progress, but distribution is a big hurdle.

Marshall-Genzer: That could be a challenge, at least in developing countries. These vaccines need to be kept very cold, below freezing. That’s not such a problem in the U.S., but could be difficult in other nations. Moderna has already agreed to supply 100 million doses to the U.S.