How ‘contagious abortion’ in cows led to one of the first known references to herd immunity

“Abortion disease may be likened to a fire, which, if new fuel is not constantly added, soon dies down,” Potter wrote in 1918, in accordance 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.”

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