this is different for each disease based on how quickly it transmits.
for SARS-COV-2 you need around 70% immunity in the population to achieve herd immunity
for SARS-COV-2 you need around 70% immunity in the population to achieve herd immunity
This is the required immunity of the population, but not the effectiveness of the vaccine. Inside the population there are groups that you cannot put the vaccine (smallest babies, immunosuppressed people, etc).