herd immunity
"The idea of herd immunity is like a moat around a castle or the natural behavior of herd animals when threatened by a predator. The strong surround the weak to protect them from attack; in this case the vaccinated protect those who can't be vaccinated or those with low immunity from contact with the flu by halting the spread of the virus."
"Herd immunity is like clearing your backyard of brushes," he said. "So every person that has antibodies to the virus, either through the vaccine or being infected previously, those are people that can no longer burn."
"Herd immunity" is like what makes it hard to learn Chinese in a town where very few people are learning Chinese. There are few tutors. The second hand bookshops don't have cheap beginners textbooks. You don't hear Chinese on the radio or TV.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.