Herd immunity is a topic that has often come up as a possible way to end the COVID-19 pandemic. And, while numbers have been thrown around in the past about what part of the population needs to be vaccinated or infected to achieve herd immunity, top public health officials say it’s simply unlikely to happen. occur at this stage.
In a new article published in the Journal of Infectious Diseases, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID) and other NIAID scientists write that “classic” herd immunity for COVID-19 “is almost certainly an unattainable goal.” Dr. Fauci and his co-authors specifically cite “significant obstacles” like “substantial resistance to efforts to control the spread” of SARS-CoV-2, the virus that causes COVID-19, as public resistance to vaccination and wearing a mask.
They also note that “neither infection nor vaccination appears to induce sustained protection against SARS-CoV-2 in many or most people,” making it difficult to completely prevent COVID-19, even if you have been vaccinated or infected with the virus in the past.
But what is herd immunity, exactly, and why is it so hard to achieve with COVID-19? Here’s what you need to know.
What is herd immunity?
According to the Centers for Disease Control and Prevention (CDC), herd immunity, or population immunity or community immunity, is what happens when a significant portion of a population develops immunity against an infectious disease. This can happen through vaccination or previous infection with a particular disease, according to the CDC.
Once herd immunity in a population is achieved, an infectious disease is unlikely to spread from person to person. Herd immunity also offers protection to unvaccinated people, such as newborns, because the disease cannot spread easily in a community, the CDC explains.
Herd immunity is tricky with Omicron, Delta and other variants
Dr. Fauci and his co-authors pointed out that SARS-CoV-2 continues to develop variants, making it difficult to develop herd immunity against it. “This is a mutating virus – we get new subvariants all the time,” says William Schaffner, MD, an infectious disease specialist and professor at Vanderbilt University School of Medicine. “It is very difficult to achieve sufficient population immunity where this transmission of the virus is completely interrupted.”
Infectious disease expert Amesh A. Adalja, MD, principal investigator at the Johns Hopkins Center for Health Security, agrees. “SARS-CoV-2 is not as genetically stable as other pathogens, such as measles, against which herd immunity has been achieved,” he says. “The virus comes from a viral family known to mutate to be able to routinely re-infect individuals.”
As a result, says Dr. Schaffner, “we can’t do with COVID-19 what we did with measles.”
Can we achieve herd immunity against COVID-19 through natural infections?
Natural infections, as well as vaccines, can lead to herd immunity in a population, but that’s hard to achieve with COVID-19, says Thomas Russo, MD, professor and chief of infectious diseases at the University at Buffalo in New York. “New variants keep popping up,” he says.
And, even if someone develops infection-acquired immunity by catching COVID-19, it’s likely they’ll only be immune to that particular variant, Dr. Russo says. So if you have been infected with Delta, it is still possible to be infected with Omicron. “Our ability to move forward and build a level of immunity in the population to eradicate this virus is really not achievable, either through infection or vaccines,” he said. he.
Dr. Russo also points out that SARS-CoV-2 can also live in animals, where it can continue to mutate and then spread to humans. “It can also be problematic,” he says. “Even if we are able to handle infections in humans – which we really won’t be able to – more than 20 animals can support virus replication. This is another huge hurdle.
Dr. Fauci on herd immunity
Dr. Fauci has talked about herd immunity before, and he originally thought that might be an achievable goal with COVID-19.
Dr Fauci once said that 60% to 70% of the population should be vaccinated to achieve herd immunity, but he said The New York Times in December 2020 that the number is probably closer to 90%. “We have to be humble here,” he said at the time. “We really don’t know what the real number is. I think the real range is between 70 and 90%. »
Now, he wrote in the diary, that’s just unlikely to happen. “If vaccine-induced immunity or infection against SARS-CoV-2 indeed turns out to be short-lived, or if escape mutants continue to emerge, viral spread may continue indefinitely, although hopefully at a low endemic level,” he and his co-authors said.
What happens next with COVID
COVID-19 is not going anywhere, and Dr Adalja says it was “always destined” to become a “community-acquired seasonal respiratory coronavirus”.
Dr. Russo says he expects COVID-19 to eventually be similar to the flu. “We will have intermittent bumps and expect cases to be mostly asymptomatic or mild disease,” he says. “We will manage it and do our best to control it through vaccination.”
Dr Schaffner says it is likely that “periodic boosters” will be needed which “will need to be modified and adapted as the virus evolves in our population”.
“We may need to get an Omicron booster in the fall or winter, it wouldn’t surprise any of us,” he says. “The big challenge is getting the public to accept it.”
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