Bracing for a future without herd immunity

For many months after the coronavirus locked the world into a strange and fearsome new reality, herd immunity was billed as the key to our escape. Vaccinate enough of the population, the theory went — between 60% and 70%, it was estimated — and the virus would no longer be able to spread widely. But recently, the tantalising promise of a clean exit from the pandemic has receded. “There is consensus among scientists and public health experts,” The Times wrote two weeks ago, “that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever.”

How did herd immunity come to be seen as a remote possibility, and what does a future without it look like? Here’s what people are saying. Is this all because too many Americans don’t want to get vaccinated? Vaccine hesitancy is certainly a major factor in the vaccination slowdown — but it’s not the only one. While 28 million American adults remain outright opposed to getting vaccinated, an even larger number — 30 million Americans, or about 10% of the population — say they are open to getting vaccinated but haven’t yet managed to do so, according to an analysis of U.S. census data. This “vaccine amenable” population is predominantly working class, and many of its members have scarce free time and cannot afford to take time from work if they experience side effects.

Dr. Tom Frieden, a former director of the Centers for Disease Control and Prevention, believes the best way to increase uptake among this population is simply to make the vaccine more accessible. “That means walk-in hours,” he said last week. “That means easy locations, easy hours, supporting transportation and setting up pop-up sites outside of everywhere, from ballgames to bars to bowling alleys to shopping centers.”

But even if the United States could vaccinate a large majority of its population, global obstacles to herd immunity are likely to remain. The initial estimate for the herd immunity threshold was made before the appearance of the much more contagious B.1.1.7 variant, which pushed the estimate to at least 80%. If more contagious variants emerge, the estimate will increase again.

The longer the virus has to spread uncontrolled in unvaccinated parts of the world, the more opportunities it will have to develop such variants, which would inevitably make their way to the United States. And right now, the global distribution of vaccines remains staggeringly unequal, with only 0.3% of all doses administered in low-income countries. Just as vaccine access is a global problem, so is vaccine hesitancy: About 32% of adults worldwide — or 1.3 billion people — said they would not take the vaccine, according to a Gallup poll released this month.

All of these factors make global elimination of the coronavirus an unlikely prospect: A January survey conducted by the journal Nature of more than 100 immunologists, infectious-disease researchers and virologists found that about 90% expected the coronavirus to become endemic, meaning it will circulate at a constant level around the world for years to come.

Does this mean life will never return to normal? No. Many experts now say that the fixation on herd immunity as the only path back to normalcy is misguided. “Achieving herd immunity is a matter of numbers and can become a distraction from what people actually care about,” Abraar Karan, a global health physician at Brigham and Women’s Hospital and Harvard Medical School, and Julie Parsonnet, an epidemiologist at Stanford, write in The Washington Post. “For many people, it’s more important to see loved ones without worry or to live without having to wear masks in public spaces.”

The history of previous pandemics here is instructive: In the case of the 1918 flu, the world didn’t even have a vaccine. Nor did humans develop so-called natural herd immunity, which Howard Forman, a public-health professor at Yale, told The Atlantic has never been achieved for any disease. Rather, Helen Branswell explains in Stat, as more and more people became immune to the 1918 virus, it evolved, bequeathing milder versions that still circulate today. “The truth of the matter is that pandemics always end,” Branswell writes. “And to date vaccines have never played a significant role in ending them.”

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. 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. 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.

Many scientists are preparing for this possibility. Dozens of research teams are now working on creating a universal coronavirus vaccine that could protect against variants not yet in existence, a race that Dr. Fauci told The Atlantic could yield a winning candidate even before the pandemic ends.

Spencer Bokat-Lindell is a journalist with NYT©2021

The New York Times