Why some say to forget the term 'herd immunity'

Registered nurse Jessica Hack prepares a Moderna COVID-19 vaccine at the Mountain America Exposition Center in Sandy on Tuesday, May 18, 2021. (Photo: Scott G Winterton, Deseret News )

(Scott G Winterton, Deseret News)



SALT LAKE CITY — Remember when getting enough Utahns vaccinated against COVID-19 was going to stamp out the deadly disease once and for all, thanks to reaching what's known as herd immunity?

Now experts say that's not likely to happen here or anywhere else.

Around half of Utahns are considered immune to COVID-19, with just over 36% of the population fully vaccinated against the virus, and confirmed cases represent about another 13%. Estimates of what level would mean herd immunity against the coronavirus have ranged from as low as 60% to 90% or even higher.

But hitting the herd immunity target for COVID-19 may be all but impossible. The emergence of more contagious variants of the virus suggest the percentage of the population that needs protection should be at the high end of the range, especially since those who've previously had the disease may be vulnerable to the new strains.

And virus vaccinations have slowed in Utah and elsewhere in recent weeks. A recent Deseret News/Hinckley Institute of Politics poll found that 17% of Utahns are either in a wait-and-see mode when it comes to getting the shots or in no hurry, while 13% say they'll never get the vaccine.

Phrase has caused confusion

Even Dr. Anthony Fauci, the Biden administration's top adviser on the virus, says it's time to stop talking about herd immunity.

"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," Fauci told the New York Times. "That's why we stopped using herd immunity in the classic sense."

His advice? "Forget that for a second. You vaccinate enough people, the infections are going to go down."

Utah lawmakers were told to think of herd immunity as a shield against COVID-19 during a presentation to the Legislature's Health and Human Services Interim Committee earlier this week by Melissa Diamond, assistant director of the Utah Department of Health's division of disease control and prevention.

Diamond defined herd immunity as a high enough level of immunity that "most infected people will only have contact with immune people." Immunity comes from both already having had a disease as well as being vaccinated against it.

"In herd immunity, people who are immune become shields, preventing the virus from using them to continue the transmission chain to another person," she said. "Herd immunity doesn't mean people stop being susceptible to infection. It means more people act as shields to prevent the spread of infection."

When it comes to COVID-19, however, Diamond said it's not yet known what herd immunity should look like. So, she said, it's a "really challenging concept" to put a number on how many Utahns need to be vaccinated to reach herd immunity.

Siqi Pang, 12, looks away as Sean Murphy gives her a COVID-19 vaccination at the Mountain America Exposition Center in Sandy on Tuesday, May 18, 2021. Min Hu ,
Siqi Pang, 12, looks away as Sean Murphy gives her a COVID-19 vaccination at the Mountain America Exposition Center in Sandy on Tuesday, May 18, 2021. Min Hu , (Photo: Scott G Winterton, Deseret News)

"We're learning about the impact of variants and reinfection," Diamond said. "We know that immunity due to vaccines protects against known variants and produces a stronger immune response than natural infection. But we do not yet know with certainty, how long natural- or vaccine-induced immunity will last."

What the state is counting on instead of herd immunity is getting as many Utahns vaccinated as possible, she said.

A member of the committee, Rep. Robert Spendlove, R-Sandy, asked for a number anyway. After the meeting, Spendlove said he believes the state is in "a good place" since larger percentages of older Utahns more likely to become severely ill or die from the virus are fully vaccinated.

Rich Saunders, executive director of the state health department, told the committee that state officials set a target "pretty early" of vaccinating 70% of Utahns 16 and older. He said about 57.3% of that age group has received at least one dose of vaccine. They aren't fully vaccinated, however, until two weeks after their final dose.

Saunders said the department is still trying to understand the impact in Utah of last week's federal approval for 12- to 15-year-olds to be vaccinated. He said some survey information suggests only about 40% to 50% of those adolescents may get the shots. Just 11% of Utahns 12-18 are fully vaccinated.

Vaccinating children had been seen as key to reaching herd immunity against COVID-19 in Utah, the youngest state in the nation. Almost 30% of Utah's population is under 18, while just over 22% of the entire United States is that young.

But Dr. Andrew Pavia, chief of pediatric infectious diseases at the University of Utah and director of epidemiology at Intermountain Primary Children's Hospital in Salt Lake City, said recently it's time to stop aiming for a goal that is not likely to be achieved.

"I think the term herd immunity has been so abused that as an epidemiologist who learned about herd immunity and talks about it a lot, I think we need to retire it. We are probably not going to some magic point of herd immunity where the virus cannot spread anymore," he said. "I just don't think that's a useful concept anymore."

Instead, Pavia also said the focus should be simply on increasing vaccinations to slow the virus down.

"The higher level of community immunity we can reach, the less threat there will be, the less restrictions we need on our activities, the less chance that we'll have new surges with cold weather or with variants coming through," he said, adding that still means "a significant portion of children" need to be vaccinated.

He said in the past few weeks, research has shown that one factor in herd immunity, having had the disease, does not appear to provide as much protection against COVID-19 variants as the vaccines. So people infected with the virus months ago can still contract the new, more contagious variants and may become seriously ill.

Dr. Todd Vento, an Intermountain Healthcare infectious diseases specialist, said the new recommendations by the Center for Disease Control and Prevention allowing the fully vaccinated to stop wearing masks and taking other precautions against the virus may mean it will take longer to get to the point where the spread stalls.

"We start peeling back all those measures, we start gathering, having concerts, and you add that to a relatively low vaccination rate, then we will have a harder time getting to this concept of herd immunity," Vento said, adding he, too, doesn't want that to be anyone's focus.

"I would tell folks this: 'Don't fixate on what the number is. We know a rough range of how many folks in a population should probably be vaccinated to try to get to what this concept of herd immunity is. But more importantly, just focus on the fact that we have a very effective and very safe arsenal of vaccines," he said.

Vials of Moderna’s COVID-19 vaccines sit on a table at
the Mountain America Exposition Center in Sandy on Tuesday, May 18,
2021.
Vials of Moderna’s COVID-19 vaccines sit on a table at the Mountain America Exposition Center in Sandy on Tuesday, May 18, 2021. (Photo: Scott G Winterton, Deseret News)

Getting people vaccinated still best way to control coronavirus

Rather than eradicating COVID-19, Vento said both vaccines and continuing public health measures when necessary will help contain the virus, making it more like the flu, a disease that hasn't gone away but is controlled through annual shots that reflect the strains circulating.

Dr. Sankar Swaminathan, University of Utah Health Division of Infectious Diseases chief, said he wished there hadn't been so much attention paid to herd immunity.

"The problem is it was sort of set up as this magical goal, where we could reach some magic number and then we could just act as if there was no COVID. I think that was a disservice in a way because getting to that magic number shouldn't be the goal," Swaminathan said.

That's why public health officials have shifted their focus to increasing vaccinations, he said.

"You can't hold out false rewards as an enticement for doing something. I think you have to be realistic," the doctor said. "Nobody really knew what they meant when they said herd immunity. If you talked to experts even, they would differ on what they consider herd immunity to be."

From him, what's key is boosting vaccination rates among all groups, including underserved communities that have not been gotten the shots for a variety of reasons such as access. Otherwise, Swaminathan said, there's a risk of new, even more virulent variants developing as the virus continues to spread.

That's especially threatening to those who are immunocompromised due to organ transplants, chemotherapy or other medical issues, he said.

"We'll get there, hopefully," Swaminathan said, adding, "Every person that gets vaccinated is doing something that nobody else can do to help the poor and vulnerable in our society."

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Lisa Riley Roche

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