Herd immunity

Martina Feichter studied biology with an elective subject pharmacy in Innsbruck and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her to this day. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for since 2007 - first as an editor and since 2012 as a freelance writer.

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Herd immunity protects the unvaccinated: If a sufficient number of people in the population are vaccinated against a pathogen, the lower the risk of infection for those who have not received a vaccination because of their age or an underlying disease - for example babies. In addition, herd protection through vaccination can aim to eradicate a disease in the long term. Read everything you need to know about herd immunity here!

What is Herd Immunity?

Herd immunity for an infectious disease is given when so many people in a population have become immune to the pathogen thanks to vaccination (or previous infection) that the disease can barely spread. Then individual people with a lack of immunity are largely protected from infection.

If isolated infections do occur, they can hardly spread - the pathogen "hits" in its environment mainly on immune people to whom it cannot harm - and who therefore do not pass the pathogen on. The chain of infection breaks off.

Herd immunity is also called herd protection or community protection.

Aim: to protect the unvaccinated

When herd immunity for a certain infectious disease is achieved, one primarily protects those people who cannot be vaccinated against the pathogen in question - for example because of their age or a chronic illness. This can be, for example, babies, pregnant women or people with an immune deficiency (e.g. due to old age or chemotherapy).

Vaccination opponents and their unvaccinated children also benefit from herd protection through vaccination: If most people have received the vaccination they have rejected all around, i.e. cannot become infected with the pathogen and pass it on, they themselves are largely protected from infection.

Goal: Eliminate an infectious disease

Programs that aim to protect herds through vaccination can, in addition to the direct protection of individual unvaccinated persons, also have a long-term goal - "extermination", i.e. the elimination of the infectious disease in question in the population.

A disease is considered to be eradicated if there is less than one disease per million inhabitants under an ongoing vaccination program. In Germany, this has been successful with poliomyelitis (polio for short):

The last report of a polio disease acquired in Germany by a wild virus comes from the year 1990. In other countries (such as Egypt, India) the disease still occurs and can be introduced to Germany from there. In order to prevent such introduced outbreaks and to maintain herd immunity, vaccination against polio continues in this country - until polio is eliminated worldwide.

Such a global eradication has so far been successful in the case of "pox", thanks to a global vaccination campaign by the World Health Organization (WHO).

When is herd immunity achieved?

Herd immunity - more precisely herd protection through vaccination - is only given when the so-called vaccination coverage has reached a certain level. This is the percentage of people in a population who have been vaccinated against the pathogen in question.

How high this vaccination rate must be depends on the infectiousness of the pathogen - i.e. how contagious it is: the more infectious a pathogen is, the higher the vaccination rate must be for herd immunity.

The aim is a vaccination rate of 95 percent for the very contagious measles virus. From then on, herd immunity is given, which also protects those people from infection who cannot be vaccinated (such as very young infants). In the case of the less contagious infectious disease diphtheria, this should be possible from a vaccination rate of around 80 percent.

In general, the vaccination rate necessary for herd immunity fluctuates between 75 and 95 percent depending on the infectiousness of a pathogen.

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