Moderna Vaccine Offers Possible Antidote to Deep-Freeze Problem

One of the biggest challenges to delivering a promising coronavirus vaccine based on unprecedented technology to millions around the world just got easier.

When Pfizer Inc. announced effective preliminary results for its vaccine candidate last week, the downside was that it must be stored at ultra-cold temperatures, posing significant logistical issues. But Moderna Inc. on Monday one-upped its rival, offering a vaccine based on the same technology that appears to be equally effective, but which also can be stored at regular refrigerated temperatures for up to a month.

The difference is significant. Delivering normal vaccines to populations in the...