Do you live in an area where a lot of people are protected against a specific virus? If you do, your community may have ‘herd immunity’.

Herd immunity is when a community as a whole is protected from a contagious disease because many of the people who live there each have protection from it⁽¹⁾ and, therefore, cannot pass the infection onto others. Unable to pass from one person to the next, the virus finds it difficult to spread.

How herd immunity works

A virus spreads when one infected person infects other people they come into contact with; then those people infect others that they come into contact with⁽²⁾.

Imagine living in a community where protection against a specific virus is low. Someone becomes ill. Most of the people they encounter are not protected. They pass the virus on with ease⁽³⁾. The disease spreads quickly through the community.

Now imagine living in a community where protection against a specific virus is high. Someone becomes ill. Most of the people they encounter are protected. The virus is unable to spread⁽³⁾. The disease disappears quickly, keeping the whole community well.

Why is herd immunity important?

With herd immunity, well-protected people are also helping to protect vulnerable members of the community⁽⁴⁾; the elderly, the very young, pregnant women and people living with chronic diseases⁽⁴⁾, in particular.

Their lack of protection may be for one of several reasons. It may be because they are unable to get vaccinated for medical reasons⁽²⁾. Or it may be because a vaccine does not work well for them⁽⁴⁾, for instance.

Herd immunity and vaccination

Vaccination protects individuals directly and communities indirectly by reducing transmission⁽⁵⁾. However, herd immunity does not give us as individuals the same high level of protection as vaccination⁽³⁾. Avoiding vaccination and just relying on indirect protection through herd immunity is, therefore, not a good alternative to getting a flu shot.

For the flu, research has shown that at least 70% of people in a community need to get an annual flu shot for herd immunity to be reached⁽²⁾. Have you had yours?

References
(1) https://www.ovg.ox.ac.uk/news/herd-immunity-how-does-it-work
(2) https://www.reuters.com/article/us-health-vaccines-education/explaining-herd-immunity-may-convince-more-people-to-get-flu-shots-idUSKBN1JW2MC
(3) https://vk.ovg.ox.ac.uk/vk/herd-immunity
(4) https://www.tandfonline.com/doi/full/10.3109/00365548.2011.582247
(5) https://www.sciencedirect.com/science/article/pii/S0264410X18306571