the.com/herd immunity
the virus runs out of new bodies to invade because everyone nearby is already armored.
means when enough of a population is immune to a disease that its spread slows or stops, protecting even the unvaccinated few.
from the term emerged from 1920s livestock studies, when researchers noticed disease outbreaks fizzled once a critical share of a herd had recovered and gained immunity, and the logic was later extended to humans.
threshold variesmeasles needs about 95 percent immune, polio around 80
math driverdepends on r naught, how contagious a disease is
protects the vulnerableshields infants and immunocompromised who cannot be vaccinated
can collapsewaning immunity or new variants can break the threshold
for instance
smallpox eradication — global vaccination ended natural transmission by 1980
uk measles resurgence — vaccine hesitancy dropped coverage below 90 percent in 2010s
sweden covid gamble — 2020 attempt to reach it naturally without lockdowns