How 'good' does a Covid-19 vaccine need to be to stop the pandemic?

To stop the pandemic, the number of new infections per day needs to drop to zero, or at least to a very low number, as quickly as possible

The U.S. is pinning its hopes on a Covid-19 coronavirus vaccine, but will a vaccine alone be enough to stop the pandemic and allow life to return to normal?

The answer depends on a how “good” the vaccine ends up being.

In a study published July 15 in the American Journal of Preventive Medicine, my colleagues and I used a computer simulation of every person in the country to show how effective a vaccine would have to be and how many people would have to get vaccinated to end the pandemic. We found that a coronavirus vaccine’s effectiveness may