COVID-19 herd immunity is a mirror image. This way, the virus can instead become ‘manageable’.

America is coming this close to herd immunity.

In May last year, “we had enough vaccination and natural immunity to have almost almost reached a population level of immunity,” said Dr. Eric Topol. “We were coming down to fewer than 10,000 cases a day. We looked good. ”

Then the delta variant moved the goal posts.

With the original version of the virus causing COVID-19, America’s current vaccination rate of around 65% would have been enough to stop the spread.

“If we were dealing with the original, we would have enough vaccination for the great pandemic to be over in this country,” said Dr. Joshua Schiffer, a physician and mathematical modeling expert studying infectious diseases at the Fred Hutchinson Cancer Research Center in Seattle.

Unfortunately, the now dominant delta strain is more than twice as contagious and requires more people to be immune through vaccination or previous infection for the virus to stop spreading, experts say.

“Now we need 85 to 90% vaccinated against delta,” said Topol, vice president of research at Scripps Research in La Jolla, California, and a national expert in the use of data in medical research.

That’s not an impossible number. In countries such as Portugal, Singapore and the United Arab Emirates, up to 80% of the total population is now vaccinated and cases and deaths are falling.

‘Can’t believe we’re here’: 700,000 US COVID-19 deaths are a milestone we never expected to reach

It seems unlikely to happen in the United States, where only 55% of the total population is fully vaccinated and 12% of Americans say they are strongly against it.

Crew immunity is now effectively out of reach, said Stephen Kissler, an infectious nurse at the Harvard TH Chan School of Public Health.

“I do not think it is realistic,” he said.

What is herd immunity?

The concept of herd immunity is simple: When disease sweeps through a herd of animals, those who survive become immune. Eventually, it probably has what is known as natural immunity, and the disease has so few animals left to infect that it dies or settles.

The concept got a lot of pressure early in the pandemic, as various politicians and even nations suggested that if young, healthy people got mild cases and recovered, there would be enough immunity that the virus would no longer circulate and vulnerable people would be protected.

This was before vaccines were available, and Britain, Sweden, Brazil and the United States under the Trump administration supported the idea to varying degrees.

At one end was a group that included Florida’s now surgeon general, who in October 2020 published the Great Barrington Declaration. It called on the world to end lockdowns and other transmission prevention measures and embrace herd immunity for COVID-19 to protect the vulnerable while thriving economies.

The idea was quickly condemned. With a mortality rate of 1% at the time, COVID-19 would have had to kill 3.2 million Americans in order for enough people to be infected to reach herd immunity.

For a time, the advent of COVID-19 vaccines changed the calculation. If two-thirds of Americans had been immunized in the spring, the virus would have had so few new humans to infect that it could have largely been stopped.

Then the delta variant hit.

At the same time, new data began to show that natural immunity was not as protective as vaccination, and the benefits of shoots began to fade after about six months.

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More than a third of COVID-19 infections result in zero protective antibodies, says Dr. Mark Rupp, an infectious disease expert at the University of Nebraska Medical Center.

“I wish that was not true,” Rupp said. Many of his patients are convinced that this is all the defense they need to recover from COVID-19.

The good news is that for people who have recovered from COVID-19, a single dose of vaccine provides excellent immunity, Topol said.

“You can not repeat that with any vaccine we have,” he said. “It’s quite unusual.”

So far, Rupp has not had much success in convincing his vaccine-resistant patients to get a shot.

“I have asked people,” he said.

050319-Herd-immunity_Online

050319-Herd-immunity_Online

When does the pandemic end?

With 55% of Americans fully vaccinated and at least 30% recovering from COVID-19 at least once, how is it possible that the pandemic can still increase in so many places?

America is a large country and even a small number are many people. Although it is difficult to determine the number of people who are not exposed to COVID-19 either through infection or vaccination, experts say it probably to about 15% of the US population. That’s nearly 50 million people – plenty to still get sick of, Harvard’s Kissler said.

It also becomes clear that COVID-19 is not “one and done,” said Lauren Ancel Meyers, professor of statistics and computer science and director of the COVID-19 Modeling Consortium at the University of Texas at Austin.

Re-infection and breakthrough cases change the landscape of susceptibility as immunity declines.

On October 1, the seven-day daily COVID-19 deaths in the United States were 1,479, according to the Centers for Disease Control and Prevention.

“I think it’s humiliating that the remaining percentage, 15%, is still enough to overwhelm our healthcare system,” Schiffer said.

Experts say endemic COVID-19 can make viruses ‘manageable’

The optimistic expectation, experts say, is that the pandemic will die down and the virus will become one of the world’s many endemic viruses that continue to circulate but cause much less disease and death..

It is predicted to become an infection that still sweeps through the adult population in the winter and makes some sick, but generally only delivers serious illness to the very old, those with compromised immune systems and pregnant women who are unvaccinated, says Dr. Gregory Poland, editor-in-chief of the journal Vaccine.

“When we get to the point where everyone has been exposed or vaccinated, and if – and it’s a big if – COVID does what other respiratory diseases do, it can be a disease that can be managed,” said Jeffrey Shaman, a epidemiologist at Columbia University.

June 2021: How does COVID-19 end up in the United States?

February 2021: Health officials say the coronavirus is likely to become endemic in the next several years.

Ideally, babies and toddlers will get it several times before going to kindergarten, experts say. Too far most, COVID-19 would be mild as it is today for most young children. When they started school, they wanted a pretty strong immune system.

The COVID-19 vaccine would become one of the routine immunizations in childhood, likely requiring more doses and possible boosters if new variants emerge, experts say.

Like influenza, COVID-19 in the northern hemisphere is expected to be a disease that manifests itself in the colder months.

If they became infected, vaccinated adults would generally have mild or even asymptomatic cases. Unvaccinated adults will be at greater risk for serious illness. With age, the immune system becomes less robust, so annual COVID-19 shots would be especially important for those over 65 and those immunocompromised.

COVID-19 is also likely to continue to mutate. In some years it would be very mild, in others more severe.

COVID-19 is still evolving

But will this virus follow the typical path of others that we are going to live with?

“That’s the billion question,” Columbia’s Shaman said.

There are no guarantees with SARS-CoV-2, which can mutate so quickly. The worst case scenario is that it develops into something even more dangerous or more contagious than delta.

“The only thing that needs to happen is that there will be a new variant with a greater escape from immunity, and we will start all over again,” Poland said.

Fact check: Yes, viruses can mutate to become more lethal

Public health experts have for years been concerned about a virus with the infectiousness of SARS-CoV-2 and the mortality rate of Middle East Respiratory Syndrome Coronavirus (MERS-CoV), which is 32% lethal.

Learning to live with COVID-19 means accepting uncertainty and staying alert to what may come, said Rustom Antia, professor of population biology at Emory University.

“Blocking a miracle,” Schiffer added, “COVID will be a part of our lives for the rest of our lives.”

Contact Weise at eweise@usatoday.com

White flags representing COVID-19 deaths are planted for a project called “In America: Remember.  ”

White flags representing COVID-19 deaths are planted for a project called “In America: Remember.”

This article originally appeared on USA TODAY: Is COVID Crew Immunity Still Possible? Experts say endemic more likely

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