One by one, the cows were losing their pregnancies.
A bacterial infection known as brucellosis was spreading through herds of cattle in the United States, causing spontaneous miscarriages known as “contagious abortion.” Farmers were desperate to quell an epidemic that cost them money with each lost calf and lamb. By the 1910s, the miscarriages had become a dire threat to livestock nationwide.
While farmers killed and sold diseased animals to try to eradicate the bacteria from their herds, Kansas veterinarian George Potter had a revelation: A cow that gets brucellosis might lose its pregnancy but would then be immune. Those that survived a “contagious abortion” were actually the most valuable.
“Abortion disease may be likened to a fire, which, if new fuel is not constantly added, soon dies down,” Potter wrote in 1918, according to an article published in the medical journal the Lancet in September. “Herd immunity is developed, therefore, by retaining the immune cows, raising the calves, and avoiding the introduction of foreign cattle.”
The reference is one of the first known uses of the term “herd immunity,” David S. Jones, a professor of the culture of medicine at Harvard University, told The Washington Post. The term is relevant again as scientists debate whether the United States can reach an ambiguously defined “herd immunity” threshold at which the novel coronavirus cannot easily spark new outbreaks. With less than half of the population having received at least one vaccine dose as demand wanes, health officials are warning that the country may never fully contain the pathogen.
Whether the United States achieves herd immunity may depend on whether health officials can get shots into the arms of people with limited access to vaccinations and, perhaps more challenging, the roughly 40 percent of Republican-leaning adults who say they do not plan to be vaccinated.
Potter’s concept spread across the United States and Britain after the veterinarian used the term “herd immunity” in reference to livestock. British scientists desperate to prevent battlefield wound infections during World War I inspired a new field of disease ecology aimed at understanding how an infection’s virulence, and a population’s immunity, make epidemic waves rise and fall, Jones wrote in the Lancet.
That field of science became popular in the 1920s, and researchers started intentionally sickening mice to map how the infection spread through their colonies. Jones said they discovered that there was some threshold above which a disease could not find new hosts and was unable to spread.
Researchers wondered whether the concept applied to humans. In 1923, British pathology professor Sheldon Dudley decided to examine a diphtheria outbreak at the Royal Hospital School in Greenwich, where Jones said 1,000 children of naval officers ate in a gargantuan dining hall and slept in crowded military-style barracks in the London borough.
Dudley found that every time new students joined the school, diphtheria, a serious infection caused by poison-producing bacteria, would latch onto those susceptible teenagers and rage through the student body again, Jones said. The conclusion led Dudley to apply the term “herd immunity” to humans in 1924 for what may have been the first time.
“In the midst of his research, a diphtheria vaccine is developed,” Jones said. “So he starts to think about, ‘How do you get to herd immunity — natural exposure or vaccination?’”
By the 1930s, herd immunity was a common concept in epidemiology and was discussed in reference to influenza, polio and other diseases. The idea was also applied to false ideas of biological racial difference, with the author of one journal article wondering whether specific groups had “racial herd immunity,” Jones wrote in his Lancet piece.
With the development of new vaccines in the 1950s and ’60s, “herd immunity” became part of the public lexicon, and public health officials eventually started citing the concept to promote inoculation campaigns, Jones said. Researchers developed a theorem in the 1970s for calculating an infection’s herd immunity threshold, according to an article in the journal Clinical Infectious Diseases.
Referring to people as a “herd” in which immunity needs to be developed, however, tends to provoke discomfort. Many people associate the idea with science-fiction novels and movies about farmed humans, Jones said, including H.G. Wells’s “The Time Machine” and “The Matrix.”
That connection, he added, may have contributed to the public’s resistance to calls from some officials last year to achieve natural herd immunity by letting the coronavirus run rampant through the population.
Jones summarized that perspective bluntly: “We don’t like to think of ourselves as livestock.”
Some have sought to overcome that mental image by trying to popularize the term “population immunity,” instead of “herd immunity.” But beyond word choices, Jones said, lies a more fundamental problem: Scientists have tended to define the concept in different ways.
Historically, some researchers understood the term to refer to the threshold above which a disease struggles to spread — the way the idea is most commonly understood now — while others thought it meant the sum of individuals’ immunity levels. One British bacteriologist, W.W.C. Topley, defined herd immunity expansively as present if the conditions in which a population lives thwarts the spread of the disease.
Jones said the term’s meaning has been unstable at every stage of its history.
“You see echoes of that now, with different people meaning different things, using it in different ways,” he told The Post. “And it’s really hard to have a concept anchoring a policy discourse if different people mean different things by the concept.”
https://www.washingtonpost.com/hist...0.hqUmPWGQKW5t4dpedHKLvQX40JXiMLoyTeOWQsF7fdg
A bacterial infection known as brucellosis was spreading through herds of cattle in the United States, causing spontaneous miscarriages known as “contagious abortion.” Farmers were desperate to quell an epidemic that cost them money with each lost calf and lamb. By the 1910s, the miscarriages had become a dire threat to livestock nationwide.
While farmers killed and sold diseased animals to try to eradicate the bacteria from their herds, Kansas veterinarian George Potter had a revelation: A cow that gets brucellosis might lose its pregnancy but would then be immune. Those that survived a “contagious abortion” were actually the most valuable.
“Abortion disease may be likened to a fire, which, if new fuel is not constantly added, soon dies down,” Potter wrote in 1918, according to an article published in the medical journal the Lancet in September. “Herd immunity is developed, therefore, by retaining the immune cows, raising the calves, and avoiding the introduction of foreign cattle.”
The reference is one of the first known uses of the term “herd immunity,” David S. Jones, a professor of the culture of medicine at Harvard University, told The Washington Post. The term is relevant again as scientists debate whether the United States can reach an ambiguously defined “herd immunity” threshold at which the novel coronavirus cannot easily spark new outbreaks. With less than half of the population having received at least one vaccine dose as demand wanes, health officials are warning that the country may never fully contain the pathogen.
Whether the United States achieves herd immunity may depend on whether health officials can get shots into the arms of people with limited access to vaccinations and, perhaps more challenging, the roughly 40 percent of Republican-leaning adults who say they do not plan to be vaccinated.
Potter’s concept spread across the United States and Britain after the veterinarian used the term “herd immunity” in reference to livestock. British scientists desperate to prevent battlefield wound infections during World War I inspired a new field of disease ecology aimed at understanding how an infection’s virulence, and a population’s immunity, make epidemic waves rise and fall, Jones wrote in the Lancet.
That field of science became popular in the 1920s, and researchers started intentionally sickening mice to map how the infection spread through their colonies. Jones said they discovered that there was some threshold above which a disease could not find new hosts and was unable to spread.
Researchers wondered whether the concept applied to humans. In 1923, British pathology professor Sheldon Dudley decided to examine a diphtheria outbreak at the Royal Hospital School in Greenwich, where Jones said 1,000 children of naval officers ate in a gargantuan dining hall and slept in crowded military-style barracks in the London borough.
Dudley found that every time new students joined the school, diphtheria, a serious infection caused by poison-producing bacteria, would latch onto those susceptible teenagers and rage through the student body again, Jones said. The conclusion led Dudley to apply the term “herd immunity” to humans in 1924 for what may have been the first time.
“In the midst of his research, a diphtheria vaccine is developed,” Jones said. “So he starts to think about, ‘How do you get to herd immunity — natural exposure or vaccination?’”
By the 1930s, herd immunity was a common concept in epidemiology and was discussed in reference to influenza, polio and other diseases. The idea was also applied to false ideas of biological racial difference, with the author of one journal article wondering whether specific groups had “racial herd immunity,” Jones wrote in his Lancet piece.
With the development of new vaccines in the 1950s and ’60s, “herd immunity” became part of the public lexicon, and public health officials eventually started citing the concept to promote inoculation campaigns, Jones said. Researchers developed a theorem in the 1970s for calculating an infection’s herd immunity threshold, according to an article in the journal Clinical Infectious Diseases.
Referring to people as a “herd” in which immunity needs to be developed, however, tends to provoke discomfort. Many people associate the idea with science-fiction novels and movies about farmed humans, Jones said, including H.G. Wells’s “The Time Machine” and “The Matrix.”
That connection, he added, may have contributed to the public’s resistance to calls from some officials last year to achieve natural herd immunity by letting the coronavirus run rampant through the population.
Jones summarized that perspective bluntly: “We don’t like to think of ourselves as livestock.”
Some have sought to overcome that mental image by trying to popularize the term “population immunity,” instead of “herd immunity.” But beyond word choices, Jones said, lies a more fundamental problem: Scientists have tended to define the concept in different ways.
Historically, some researchers understood the term to refer to the threshold above which a disease struggles to spread — the way the idea is most commonly understood now — while others thought it meant the sum of individuals’ immunity levels. One British bacteriologist, W.W.C. Topley, defined herd immunity expansively as present if the conditions in which a population lives thwarts the spread of the disease.
Jones said the term’s meaning has been unstable at every stage of its history.
“You see echoes of that now, with different people meaning different things, using it in different ways,” he told The Post. “And it’s really hard to have a concept anchoring a policy discourse if different people mean different things by the concept.”
https://www.washingtonpost.com/hist...0.hqUmPWGQKW5t4dpedHKLvQX40JXiMLoyTeOWQsF7fdg