The U.S. Department of Agri­culture (USDA) last week granted Ames-based Harrisvaccines a conditional license for the company’s vaccine to battle the swine disease porcine epidemic diarrhea virus, or PEDV. The license is the first granted to a vaccine to battle PEDV, which has killed an estimated 8 million piglets in the United States since it was first detected in the spring of 2013.

Harrisvaccines’ vaccine for PEDV, called porcine epidemic diarrhea vaccine, RNA (formally known as iPED+), has been on the market for several months, and the company has sold nearly 2 million ...