‘Unintentional’ herd-immune strategy may have curbed COVID prevalence


  • A person can gain herd immunity to enough people against the virus, either through vaccination or infection.
  • Arizona, Florida, and Texas – which had a massive coronovirus outbreak after the initial reunion – that may have reached a low of last month, which has helped slow the spread of the virus over the past month.
  • But it came at a cost of thousands of lives, and experts say it is still not enough to prevent further outbreaks if these states go back to normal life because it was a pre-pandemic.
  • Visit Business Insider’s homepage for more stories.

So many Americans have received COVID-19 that their immunity may have helped slow the spread of the virus in hotspots.

A lion of infections and deaths during America’s second coronavirus clustered in some of the quickly reopening states, including Arizona, Florida and Texas this summer. Since then, however, new cases have decreased significantly in those states, which had fallen to nearly the levels reported before the summer wave.

According to epidemiologist Trevor Bedford, this may be partly because a lot of people in those states have developed immune responses, so the virus now has more difficulty spreading. This is, in essence, a degree of herd immunity: the point at which one becomes immune to a virus to limit its ability to spread enough virus.

Herd is the safe way to gain immunity through mass vaccination. The dangerous way is largely through infection – but this usually means when people talk about “herd immunity tactics” in this epidemic.

“I certainly believe that ‘herd immunity’ strategy to deal with COVID-19 is extremely expensive in terms of health effects,” Bedford wrote Twitter last month. “But it seems that the strategy is probably going on spontaneously in some parts of America.”

Now, a month later, it seems that states such as Arizona, Florida and Texas have stumbled upon the onset of herd immunity – which may play a role in more than states’ low daily infections. But it came at a huge cost: Since May 15, at which point all three states had reopened, coronaviruses have killed more than 4,600 people in Arizona, more than 10,600 in Florida, and 12,700 in Texas. more than.

It is unclear what infection rates do for herd immunity.

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Joshua Land, Taylor Brooks and Heather Jones cocktail on June 26, 2020 at the Bernini Italian Restaurant in Tampa, Florida.

Octavio Jones / Getty Images


Epidemiologists do not know what coronovirus infection rates allow populations to access herd immunity. Typically, this ratio is determined by the number of people for whom an average infected person passes through a pathogen. For coronaviruses, it is about two to three, meaning that approximately 50–70% of people will need to be protected through vaccination to prevent the spread of the virus.

But when it comes to immunity gained as a result of infection, the dynamics of how people move and behave affects the herd’s immune range. For example, some groups of people have more interpersonal contact than others. Therefore, if large parts of those particular groups contract the virus and acquire immunity, this may significantly reduce future opportunities for the spread of the virus.

Business Insider reported that young, healthy people are more likely to get immunity and ‘cover’ the rest of the population. ‘

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Customers enjoy a meal at the Rack Billiards Sports Bar and Grill on May 4, 2020, the first day that retail stores and restaurants were allowed to reopen in most counties in Florida.

Paul Hennessy / Eicos Wire / Barcroft Media via Getty Images



For those reasons, some research has suggested that if 10–20% of the population becomes infected, it may bring herd immunity to some extent, as the virus will spread mostly to those who have the most contact with others. Huh.

Many researchers believe that the herd immunity threshold is somewhere between 20% and 70%, and that it will vary for different populations.

“I think the data we have right now (which is robust) indicates that it is> 25%,” Marm Kilpatrick, a disease ecologist and biologist at the University of California’s Santa Cruz, told Business Insider. “But it can be as low as 30%. In some it can be up to 50% [populations]. ”

Immunity levels below these thresholds can still help prevent the spread of the virus, however, even if they do not eliminate it.

Partial herd immunity may have helped level the curve in some places

New York City, where hospitals and morgues sank in March and April from the first major US COVID-19 outbreak, seems to be the first place in the country to have achieved a significant degree of immunity.

A survey by the Centers for Disease Control and Prevention detected coronavirus viruses – indicating an immune response – in 23% of New York City blood tests in late April and early May.

Similarly, Gu’s model estimates that about 25% of Florida’s population was infected by Friday. In Arizona, he estimates the portion is 24%, while in Texas it is about 23%, and in New York State, about 21%.

However, new cases in those states are not the only reason for the decline: epidemiologists also attribute behavior-change such as wearing a mask, social distinctions, and a tendency to new trade-offs.

“The behavioral effects from hepat immunity are very difficult to overcome,” Kilpatrick said.

This is because in addition to limiting the opportunities for the spread of the virus, these behavioral changes also reduce the level of herd immunity required to prevent an epidemic.

“Due to this reduction in broadcasting through social media, we do not need that much immunity to spread influence,” Bedford said.

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People attend a July 4 rally in Phoenix, Arizona to protest coronovirus restrictions.

Cheney Orr / Reuters


But they do not think that these immune levels will be enough to stop the virus from spreading if people go back to normal life.

Although outbreaks “may have left sufficient immunity to aid in controlling COVID-19 so far”, Bedford said “this level of immunity is not consistent with a complete withdrawal to social behavior as it existed before the epidemic.” . “

Swarm immunity is not a good game plan

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Graves excavate the coffin of a man who possibly died COVID-19 on May 13, 2020, in a cemetery near St. Petersburg, Russia.

Anton Vaganov / Reuters



A few weeks ago, The Washington Post reported that Scott Atlas, a neuroradiologist who worked as a top Trump advisor to the Trump administration, asked the president to reopen businesses across the country and allow the virus to spread young and healthy Was urged to pursue herd immunity. People keeping the elderly and weak in the house.

Atlas has denied this: “There is no policy of the president or administration to obtain herd immunity,” he said in a statement. “Never has such a policy been recommended to anyone other than the President or me.”

According to vaccine expert Florian Kramer, the cost of pursuing a herd-immunization strategy would be unconscious.

“Vaccination is the only way to gain herd immunity. Everything else is morally questionable,” he told Business Insider. “Would you put a vaccine that kills 1% of people who get vaccinated and protect the remaining people – but 90% of the remaining people get sick? That’s what infection does.”

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The patrons of the West Alabama Ice House own the beer on June 26, 2020 in Houston, Texas.

Mark Felix / AFP / AFP via Getty Image


Even in an optimistic scenario, in which only 20% of the population needed to be infected to reach herd immunity, about 600,000 people would still die in the US.

It does not refer to all those who will fall ill – many so severely that they will end up in the hospital. Many of those long-term symptoms will develop debility: fatigue, difficulty breathing and kidney damage to name a few.

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The medical staff pushes a stretcher with a deceased patient outside the COVID-19 intensive-care unit on June 30, 2020, at the United Memorial Medical Center in Houston, Texas.

Go Nakamura / Getty Images



“Humans are not herds,” said Michael Ryan, executive director of the World Health Organization’s Health Emergency Program. “I think we really need to be careful when we use words in this way around natural infections in humans, because it can produce a very cruel arithmetic that can affect people and life and that equation Does not suffer at the center. ”

In fact, the US has paid a steady price for some states to achieve a small degree of herd immunity through natural infections: mass deaths, overwhelmed hospitals, refrigerator trucks filled with bodies, and lack of nationwide testing.

“The cost for this immunity is substantial and is steadily increasing,” Bedford said. “We need a vaccine to achieve population immunity in a fashion that does not kill people.”

Sinéad Baker contributed to reporting this story.

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