Karen Joynt Maddox is a cardiologist and co-director of the Center for Health Economics and Policy at Washington University in St. Louis. Her research interests include improving the measurement of physician, hospital and health system quality. 

“The challenges of vaccine development do not end once an effective vaccine is identified.”

This sentiment has become abundantly clear to anyone who has followed the U.S. vaccine rollout over the last several weeks. According to Bloomberg’s Vaccine Tracker, around 11 million doses have been given so far. That’s well short of the Trump administration’s initially-announced goal of vaccinating 20 million Americans by the end of 2020, and even further short of the estimated 70-80% of Americans who will need to receive vaccines to achieve herd immunity and stop this virus.

The opening quote comes from a fascinating November 2020 paper published in Health Affairs by A. David Paltiel, Jason L. Schwartz, Amy Zheng, and future CDC Director Rochelle P. Walensky. The authors used standard epidemiologic modeling tools to simulate how different levels of epidemic severity (the amount of disease circulating in the community), vaccine efficacy (how well the vaccine protects people from the virus), and speed and completeness of vaccine implementation (how many and how quickly people will be vaccinated) would impact our ultimate control of this deadly disease.

Although the paper was published a few months ago, what the authors found could not be more timely. If rollout of a vaccine (the authors assumed 75% efficacy) were progressing at the speed many had hoped for – roughly 1% of the population per day – 58% of COVID infections could be averted at six months. At the speed the authors estimated as their “best guess,” 0.5% of the population per day (the peak speed of flu vaccination in a typical year), 35% of infections could be averted. And at roughly our current speed of vaccination (about 0.1% of the population per day), it will avert only 6% of infections in the first six months.

The authors’ calculations are complex, but their findings are intuitive: Think of the pandemic like a big fire. Having a powerful fire hose (highly effective vaccine) is great, but its usefulness depends a lot on how quickly the fire department can respond (speed of vaccine rollout). (H/t to The New York Times’ David Leonhardt for the fire hose analogy.)

This study underscores just how catastrophic a continued slow vaccine rollout will be and how important it is to not assume that a highly effective vaccine on its own will save us. Policymakers need to do whatever they can to speed up the process of getting vaccines into the arms of all those who want them, and we all need to redouble our efforts to limit the spread of the virus — so that the vaccine can be as effective as possible.