What is ‘herd immunity’?
‘Herd immunity’, also known as ‘population immunity’, is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached.
Herd immunity is achieved by protecting people from a virus, not by exposing them to it.
Vaccines train our immune systems to create proteins that fight disease, known as ‘antibodies’, just as would happen when we are exposed to a disease but – crucially – vaccines work without making us sick. Vaccinated people are protected from getting the disease in question and passing it on, breaking any chains of transmission. Visit our webpage on COVID-19 and vaccines for more detail.
With herd immunity, the vast majority of a population are vaccinated, lowering the overall amount of virus able to spread in the whole population. As a result, not every single person needs to be vaccinated to be protected, which helps ensure vulnerable groups who cannot get vaccinated are kept safe.
The percentage of people who need to have antibodies in order to achieve herd immunity against a particular disease varies with each disease. For example, herd immunity against measles requires about 95% of a population to be vaccinated. The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated. For polio, the threshold is about 80%.
Achieving herd immunity with safe and effective vaccines makes diseases rarer and saves lives.
Find out more about the science behind herd immunity by watching or reading this interview with WHO’s Chief Scientist, Dr Soumya Swaminathan….read more.