As I understand it, quarantine is used to describe the isolation of the infected to prevent spread of infection. However, I'm looking for a word for the isolation of the healthy to avoid infection.
There's no single directly fitting antonym, however, there are a few options to convey your meaning:
- Reverse quarantine - this uses negation to create the meaning
- Isolation - this conveys the general meaning, and can be used in a medical context
- Protective sequestration - this fits best with your intended meaning, "isolating a still-healthy population to prevent diesease from spreading to it"
When the infected are quarantined, the healthy are insulated.