Herd immunity

This population effect is called herd immunity. It can indirectly protect people who are not immune, including some people who cannot be vaccinated. Imagine a chain in which one infected person would otherwise transmit a pathogen to several others.

If the same pathogen is encountered later, the immune response can be faster and larger, so the pathogen is less likely to cause disease. This provides the foundation for both individual protection and herd immunity, although vaccination does not produce immunity in every person.

When a large proportion of a population is vaccinated, chains of transmission are more likely to be interrupted. This is called herd immunity.

This population effect is called herd immunity. It gives some indirect protection to people who are not immune because they are less likely to encounter an infected person. This is particularly important for people who cannot receive a particular vaccine, or whose immune response is weak.