What is Herd Immunity?

Herd immunity describes how a population is protected from a disease after vaccination by stopping the pathogen responsible for the infection being transmitted between people. In this way even people who cannot be vaccinated, for example very young children, can be protected. However, for herd immunity to work, a large proportion of the population need to be vaccinated.

Watch this animation made by Vaccines Today showing how herd immunity works:

This is an additional video, hosted on YouTube.

However, when immunisation rates fall, herd immunity can break down leading to an increase in the number of new cases. For example, recent outbreaks of measles in the UK & US and pertussis in the US have been attributed to declining herd immunity. We will look at this again in week 2.

Watch this TED talk by Professor Adam Finn which describes how vaccines work and why we all have a role in ensuring that they are effective. Recorded at TEDMEDLive Bristol April 2013:

This is an additional video, hosted on YouTube.

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The Role of Vaccines in Preventing Infectious Diseases and Antimicrobial Resistance


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