On December 23, as part of a publicity push to encourage people to get vaccinated against covid-19, the University of Pennsylvania released footage of two researchers who developed the science behind the shots, Katalin Karikó and Drew Weissman, getting their inoculations. The vaccines, icy concoctions of fatty spheres and genetic instructions, used a previously unproven technology based on messenger RNA and had been built and tested in under a year, thanks to discoveries the pair made starting 20 years earlier.

The infection has killed more than 2 million people globally, including some of Weissman’s childhood friends. So far, the US vaccine campaign has relied entirely on shots developed by Moderna Therapeutics of Cambridge, Massachusetts, and BioNTech in Mainz, Germany, in partnership with Pfizer. Both employ Weissman’s discoveries. (Weissman’s lab gets funding from BioNTech, and Karikó now works at the company.)

Unlike traditional vaccines, which use live viruses, dead ones, or bits of the shells that viruses come cloaked in to train the body’s immune system, the new shots use messenger RNA—the short-lived middleman molecule that, in our cells, conveys copies of genes to where they can guide the making of proteins.

Pivoting to vaccines did have a drawback for Moderna. Andrew Lo, a professor at MIT’s Laboratory for Financial Engineering, says that most vaccines lose money. The reason is that many shots sell for a “fraction of their economic value.” Governments will pay $100,000 for a cancer drug that adds a month to a person’s life but only want to pay $5 for a vaccine that can protect against an infectious disease for good. Lo calculated that vaccine programs for emerging threats like Zika or Ebola, where outbreaks come and go, would deliver a -66% return on average. “The economic model for vaccines is broken,” he says.

On the other hand, vaccines are more predictable. When Lo’s team analyzed thousands of clinical trials, they found that vaccine programs frequently succeed. Around 40% of vaccine candidates in efficacy tests, called phase 2 clinical trials, proved successful, a rate 10 times that of cancer drugs.