the.com/herd immunity
the virus runs out of strangers to infect because everyone it meets is already armed.
means a population gains collective protection from a disease once enough individuals are immune, breaking the chains of transmission that would otherwise let it spread.
from coined by veterinarians and epidemiologists studying livestock in the early 1900s, who noticed disease outbreaks in herds fizzled once enough animals had recovered or were vaccinated, denying the pathogen fresh hosts.
threshold variesmeasles needs 95 percent, polio needs about 80
not absolutepockets of susceptible people can still flare up
protects the vulnerableshields newborns and immunocompromised who cannot vaccinate
for instance
smallpox eradication — global vaccination campaign wiped it out by 1980
uk measles resurgence — 2019 lost elimination status after vaccination rates dipped
sweden covid strategy — 2020 gamble on natural immunity without lockdowns, contested results