How the measles outbreak spreads when kids get vaccinated – and when they don't

A majority of the infections during measles outbreaks are unvaccinated people. Only very highly vaccinated groups are able to consistently block measles infection from their community, showing just how important high rates of immunization can be. The graphic below presents 6 hypothetical communities with different vaccination rates and illustrates how herd immunity works. All the dots represent people who are the same or similar ages, such as school children. There are no babies or non-immune elderly folks in our examples, but there are some children who can’t get the vaccine for medical reasons.

The sample children above are in close contact and they mix randomly and they each have an equal chance of coming into contact with someone from the outside world who is infected with measles – the incoming red dots. Measles is extremely infectious - the simulation below shows how it spreads within a community.