https://www.sciencedaily.com/releases/2020/11/201119131035.htm > Billions of dollars have been spent on developing COVID-19 vaccines, and preliminary evidence suggests that several candidates appear to be extraordinarily effective. "But there are lots of ways to think about the effectiveness of a vaccine," says Walensky. She teamed up with A. David Paltiel, PhD, a professor of Public Health (Health Policy) at the Yale School of Public Health (YSPH), and several other colleagues to create a mathematical model that assessed how other factors beyond a COVID-19 vaccine's efficacy might influence how well it thwarts the disease. Those factors included: > The mathematical model considered how these factors would influence the impact of vaccines of varying levels of efficacy. "We found that infrastructure will contribute at least as much to the success of the vaccination program as will the vaccine itself," says Paltiel. "The population benefits of vaccination will decline rapidly in the face of manufacturing or deployment delays, significant vaccine hesitancy, or greater epidemic severity."