ANALYSIS: What If We Never Reach Herd Immunity?

What If We Never Reach Herd Immunity? Hitting the threshold might actually be impossible. But vaccines can still help end the pandemic. Sarah Zhang The Atlantic

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. The COVID-19 vaccines as a whole are excellent at preventing severe disease, and this level of protection so far seems to hold even against a new coronavirus variant found in South Africa that is causing reinfections. This, rather than herd immunity, is a more achievable goal for the vaccines. “My picture of the endgame is we will, as fast as we can, start taking people out of harm’s way” through vaccination, says Marc Lipsitch, an epidemiologist at Harvard. The virus still circulates, but fewer people die.

At the same time, we don’t need to hit the herd-immunity threshold before transmission begins to slow. With less transmission, fewer people will get exposed, and if those who do are vaccinated, even fewer will become seriously sick or die. The pandemic will slowly fade as hospitalizations and deaths inch down.

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.

The variants are the newest and potentially most pressing challenge to herd immunity. As the virus evolves, our vaccines and our immunity will continually have to catch up. “The trillion-dollar question for where we go from here is this relationship we have with the variants,” says Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota. ...