NY Times: We're probably not going to reach herd immunity in the US

The NY Times reports that experts now believe we’re unlikely to reach herd immunity here in the United States. A combination of vaccine hesitancy and variants may have put that out of reach.

More than half of adults in the United States have been inoculated with at least one dose of a vaccine. But daily vaccination rates are slipping, and there is widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever.

Last year when we first started talking about the possibility of herd immunity, the best estimate was that we’d reach that point once 60-70% of the population had either recovered from the disease or been vaccinated. But those estimates were based on the original virus, not the variants that are now dominant in the US and elsewhere.

Experts now calculate the herd immunity threshold to be at least 80 percent. If even more contagious variants develop, or if scientists find that immunized people can still transmit the virus, the calculation will have to be revised upward again.

So the basic idea here is that we probably need 80 vaccination to get to herd immunity but 30% of the US population is in the “hesitant” category. Even if that drops over time, there’s still the problem that many other countries won’t be as well vaccinated as the US for a long time. The Times reports only 2% of India has been vaccinated and about 1% of South Africa. So even as we get close to herd immunity, the rest of the world will continue to spawn variants, some of which may be more contagious and will spread here eventually.

The good news is that even if we continue to have local or regional outbreaks, the death rate from those incidents could drop and stay fairly low thanks to the fact that we have managed to vaccinate most of the vulnerable population.

By focusing on vaccinating the most vulnerable, the United States has already brought those numbers down sharply. If the vaccination levels of that group continue to rise, the expectation is that over time the coronavirus may become seasonal, like the flu, and affect mostly the young and healthy.

“What we want to do at the very least is get to a point where we have just really sporadic little flare-ups,” said Carl Bergstrom, an evolutionary biologist at the University of Washington in Seattle. “That would be a very sensible target in this country where we have an excellent vaccine and the ability to deliver it.”…

“The vast majority of the mortality and of the stress on the health care system comes from people with a few particular conditions, and especially people who are over 60,” Dr. Lipsitch said. “If we can protect those people against severe illness and death, then we will have turned Covid from a society disrupter to a regular infectious disease.”

There are all kinds of discussions being kicked around about how to induce the hesitant population to get vaccinated. Some are pushing for vaccine passports, others for mandatory vaccinations. Some are recommending some kind of PR push to appeal to the groups who are most resistant. But the ultimate inducement is already there for people over 60 and for those with preexisting conditions. Those people most likely to die from the virus should get the vaccine out of self-interest. And as long as they do, the death toll should remain relatively low even if we don’t get to herd immunity.

My memory of the outbreak last year is that even as the number of cases started to rise in February and March, most people didn’t really react until we started to see the death rate climb beyond a few isolated cases. Part of that may have been because we didn’t have enough testing to really see how quickly the virus was spreading, but I think part of it is simply that death focuses everyone’s attention.

The same could be true in reverse. If we continue to have occasional outbreaks but the death toll can be counted in single digits, then most people are going to consider that a return to normal even if, in theory, some even better condition of true herd immunity in which no one gets sick or dies is possible.