So if herd immunity isn’t achievable, what is the goal? In the medium term, well-vaccinated populations may find it possible to eliminate the virus or reduce it to a containable threat, like measles. “What we want to do at the very least is get to a point where we have just really sporadic little flare-ups,” Carl Bergstrom, an evolutionary biologist at the University of Washington in Seattle, told The Times. “That would be a very sensible target in this country where we have an excellent vaccine and the ability to deliver it.”
Depending on vaccine uptake, some parts of the country are likely to fare better than others. “As time goes along, some regions of the nation may see something close to herd immunity with very few infections, rare outbreaks and only very modest measures needed to keep infections under control,” Ashish K. Jha, the dean of the Brown University School of Public Health, writes in The Washington Post. “In states with lower rates of vaccination, we are likely to see large outbreaks that run for longer before they are contained by public health interventions.”
Other variables — population density and the prevalence of non-pharmaceutical interventions, like ventilation and masking, for example — will also determine how resistant a community is to outbreaks. As Dr. David M. Morens, a virologist and senior adviser to Dr. Anthony Fauci, told The Times, “The herd immunity for a wealthy neighborhood might be X, then you go into a crowded neighborhood one block away and it’s 10X.”
Much more could also be done to close the yawning gap in vaccine access between rich and poor countries. While the Biden administration’s newfound support for suspending vaccine patents is an important step to that end, Dr. Karan and Dr. Parsonnet say, the World Trade Organization has yet to vote on the measure, and “we still require technology transfers, provision of essential supplies and serious scaling up of vaccines in countries that have not yet seen adequate access.”
Over the coming years, experts hope the novel coronavirus will evolve to become more like the four coronaviruses that cause common colds, which frequently reinfect people but very rarely cause severe illness. With those viruses, people often get infected as children and develop partial immunity that protects them in adulthood.
“It’s not a death sentence in any way, shape or form to say we’re not going to have herd immunity,” Jennie Lavine, a biology research fellow at Emory University, told Ms. Branswell. “It just means it’s going to become endemic and then the question is, is it going to be mild and endemic, or is it going to be severe and endemic? And I would say my odds are on mild and endemic at some point. I think that seems really, really likely.”
That’s the best-case scenario. What’s the worst?
Many viruses become less deadly as they mutate, but there’s no guarantee this will happen with the coronavirus. The B.1.1.7 variant is a case in point: Several studies have suggested that it’s not only more contagious but also significantly more deadly. And while all of the major vaccines in use are highly protective against that variant, others may emerge that prove capable of escaping the vaccines’ defenses.