For COVID-19, the herd-immunity threshold is estimated to be between 60 and 90 percent. That’s the proportion of people who need to have immunity either from vaccination or from prior infection.
While COVID-19 vaccines are very good—even unexpectedly good—at preventing disease, they are still unlikely to be good enough against transmission of the virus, which is key to herd immunity. On the whole, we should expect immunity to be less effective against transmission than against disease, to wane over time, and to be eroded by the new variants now emerging around the world. If vaccine efficacy against transmission falls below the herd-immunity threshold, then we would need to vaccinate more than 100 percent of the population to achieve herd immunity. In other words, it becomes downright impossible.
Even if herd immunity remains theoretically within reach, 15 percent of Americans say they will never get a COVID-19 vaccine, making that threshold all the harder to hit.
The role of COVID-19 vaccines may ultimately be more akin to that of the flu shot: reducing hospitalizations and deaths by mitigating the disease’s severity.
We likely won’t cross the threshold of herd immunity. We won’t have zero COVID-19 in the U.S. And global eradication is basically a pipe dream. But life with the coronavirus will look a lot more normal.