In the new and urgent fight against the Zika Virus, most global health officials and policymakers are focused on immediate steps to curb the disease’s transmission. That’s important because the chances of developing a vaccine anytime soon are slim. To understand why, Health Affairs spoke with Aaron Kesselheim, an associate professor of medicine at Harvard Medical School, in the Division of Pharmacoepidemiology and Pharmacoeconomics at Brigham and Women’s Hospital, in Boston.

Kesselheim and co-author Thomas Hwang, a venture capitalist at Bain Capital, published new research in Health Affairs’ February 2016 theme issue all about vaccines. Kesselheim and Hwang’s paper examines and quantifies how the vaccine pipeline has grown over the last two decades.

We asked Kesselheim about their findings and what they mean for the global health community’s campaign to bring Zika under control. Here’s what he had to say: