[Widely circulating coronavirus variants and persistent hesitancy
about vaccines will keep the goal out of reach. The virus is here to
stay, but vaccinating the most vulnerable may be enough to restore
normalcy.] [[link removed]]

REACHING ‘HERD IMMUNITY’ IS UNLIKELY IN THE U.S., EXPERTS NOW
BELIEVE  
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Apoorva Mandavilli
May 5, 2021
New York Times
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_ Widely circulating coronavirus variants and persistent hesitancy
about vaccines will keep the goal out of reach. The virus is here to
stay, but vaccinating the most vulnerable may be enough to restore
normalcy. _

Coronavirus virion structure, SPQR10, CC BY-SA 4.0 via Wikimedia
Commons

 

Early in the pandemic, when vaccines
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the coronavirus were still just a glimmer on the horizon, the term
“herd immunity” came to signify the endgame: the point when enough
Americans would be protected from the virus so we could be rid of the
pathogen and reclaim our lives.

Now, 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.

Instead, they are coming to the conclusion that rather than making a
long-promised exit, the virus will most likely become a manageable
threat that will continue to circulate in the United States for years
to come, still causing hospitalizations and deaths but in much smaller
numbers.

How much smaller is uncertain and depends in part on how much of the
nation, and the world, becomes vaccinated and how the coronavirus
evolves. It is already clear, however, that the virus is changing too
quickly, new variants are spreading too easily and vaccination is
proceeding too slowly for herd immunity to be within reach anytime
soon.

Continued immunizations, especially for people at highest risk because
of age, exposure or health status, will be crucial to limiting the
severity of outbreaks, if not their frequency, experts believe.

“The virus is unlikely to go away,” said Rustom Antia, an
evolutionary biologist at Emory University in Atlanta. “But we want
to do all we can to check that it’s likely to become a mild
infection.”

The shift in outlook presents a new challenge for public health
authorities. The drive for herd immunity — by the summer, some
experts once thought possible — captured the imagination of large
segments of the public. To say the goal will not be attained adds
another “why bother” to the list of reasons that vaccine skeptics
use to avoid being inoculated.

Yet vaccinations remain the key to transforming the virus into a
controllable threat, experts said.

Dr. Anthony S. Fauci, the Biden administration’s top adviser
on Covid-19
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acknowledged the shift in experts’ thinking.

“People were getting confused and thinking you’re never going to
get the infections down until you reach this mystical level of herd
immunity, whatever that number is,” he said.

“That’s why we stopped using herd immunity in the classic
sense,” he added. “I’m saying: Forget that for a second. You
vaccinate enough people, the infections are going to go down.”

Once the novel coronavirus began to spread across the globe in early
2020, it became increasingly clear that the only way out of the
pandemic would be for so many people to gain immunity — whether
through natural infection or vaccination — that the virus would run
out of people to infect. The concept of reaching herd immunity became
the implicit goal in many countries, including the United States.

Early on, the target herd immunity threshold was estimated to be about
60 to 70 percent of the population. Most experts, including Dr. Fauci,
expected that the United States would be able to reach it once
vaccines were available.

But as vaccines were developed and distribution ramped up through the
winter and into the spring, estimates of the threshold began to rise.
That is because the initial calculations were based on the
contagiousness of the original version of the virus. The predominant
variant now circulating in the United States, called B.1.1.7 and first
identified in Britain, is about 60 percent more transmissible.

As a result, 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.

Polls show that about 30 percent of the U.S. population is still
reluctant to be vaccinated. That number is expected to improve but
probably not enough. “It is theoretically possible that we could get
to about 90 percent vaccination coverage, but not super likely, I
would say,” said Marc Lipsitch, an epidemiologist at the Harvard
T.H. Chan School of Public Health.

Though resistance to the vaccines is a main reason the United States
is unlikely to reach herd immunity, it is not the only one.

Herd immunity is often described as a national target. But that is a
hazy concept in a country this large.

“Disease transmission is local,” Dr. Lipsitch noted.

“If the coverage is 95 percent in the United States as a whole, but
70 percent in some small town, the virus doesn’t care,” he
explained. “It will make its way around the small town.”

How insulated a particular region is from the coronavirus depends on a
dizzying array of factors.

Herd immunity can fluctuate with “population crowding, human
behavior, sanitation and all sorts of other things,” said Dr. David
M. Morens, a virologist and senior adviser to Dr. Fauci. “The herd
immunity for a wealthy neighborhood might be X, then you go into a
crowded neighborhood one block away and it’s 10X.”

Given the degree of movement among regions, a small virus wave in a
region with a low vaccination level can easily spill over into an area
where a majority of the population is protected.

At the same time, the connectivity between countries, particularly as
travel restrictions ease, emphasizes the urgency of protecting not
just Americans but everyone in the world, said Natalie E. Dean, a
biostatistician at the University of Florida in Gainesville. Any
variants that arise in the world will eventually reach the United
States, she noted.

Many parts of the world lag far behind the United States on
vaccinations. Less than 2 percent of the people in India have been
fully vaccinated, for example, and less than 1 percent in South
Africa, according to data compiled by The New York Times.
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“We will not achieve herd immunity as a country or a state or even
as a city until we have enough immunity in the population as a
whole,” said Lauren Ancel Meyers, the director of the Covid-19
Modeling Consortium at the University of Texas at Austin.

What the future may hold

If the herd immunity threshold is not attainable, what matters most is
the rate of hospitalizations and deaths after pandemic restrictions
are relaxed, experts believe.

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.”

Over the long term — a generation or two — the goal is to
transition the new coronavirus to become more like its cousins that
cause common colds. That would mean the first infection is early in
childhood, and subsequent infections are mild because of partial
protection, even if immunity wanes.

Some unknown proportion of people with mild cases may go on to
experience debilitating symptoms for weeks or months — a syndrome
called “long Covid” — but they are unlikely to overwhelm the
health care system.

“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.”

If communities maintain vigilant testing and tracking, it may be
possible to bring the number of new cases so low that health officials
can identify any new introduction of the virus and immediately stifle
a potential outbreak, said Bary Pradelski, an economist at the
National Center for Scientific Research in Grenoble, France. He and
his colleagues described this strategy in a paper published on
Thursday
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the scientific journal The Lancet.

“Eradication is, I think, impossible at this stage,” Dr. Pradelski
said. “But you want local elimination.”

Vaccination is still the key

The endpoint has changed, but the most pressing challenge remains the
same: persuading as many people as possible to get the shot.

Reaching a high level of immunity in the population “is not like
winning a race,” Dr. Lipsitch said. “You have to then feed it. You
have to keep vaccinating to stay above that threshold.”

Skepticism about the vaccines among many Americans and lack of access
in some groups — homeless populations, migrant workers or some
communities of color — make it a challenge to achieve that goal.
Vaccine mandates would only make that stance worse, some experts
believe.

A better approach would be for a trusted figure to address the root
cause of the hesitancy — fear, mistrust, misconceptions, ease of
access or a desire for more information, said Mary Politi, an expert
in health decision making and health communication at Washington
University in St. Louis.

People often need to see others in their social circle embracing
something before they are willing to try it, Dr. Politi said.
Emphasizing the benefits of vaccination to their lives, like seeing a
family member or sending their children to school, might be more
motivating than the nebulous idea of herd immunity.

“That would resonate with people more than this somewhat elusive
concept that experts are still trying to figure out,” she added.

Though children spread the virus less efficiently than adults do, the
experts all agreed that vaccinating children would also be important
for keeping the number of Covid cases low. In the long term, the
public health system will also need to account for babies, and for
children and adults who age into a group with higher risk.

Unnerving scenarios remain on the path to this long-term vision.

Over time, if not enough people are protected, highly contagious
variants may develop that can break through vaccine protection, land
people in the hospital and put them at risk of death.

“That’s the nightmare scenario,” said Jeffrey Shaman, an
epidemiologist at Columbia University.

How frequent and how severe those breakthrough infections are have the
potential to determine whether the United States can keep
hospitalizations and deaths low or if the country will find itself in
a “mad scramble” every couple of years, he said.

“I think we’re going to be looking over our shoulders — or at
least public health officials and infectious disease epidemiologists
are going to be looking over their shoulders going: ‘All right, the
variants out there — what are they doing? What are they capable
of?” he said. “Maybe the general public can go back to not
worrying about it so much, but we will have to.”

_APOORVA MANDAVILLI is a reporter focusing on science and global
health. She is the 2019 winner of the Victor Cohn Prize for Excellence
in Medical Science Reporting. @apoorva_nyc
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