Tell Me More Series: Herd Immunity

Many of us are aware of the term ‘immunity’, which is resistance or protection against a particular infectious disease or pathogen. Over the past few years we have heard the term ‘herd immunity’ when referring to fighting an infectious disease, but what does herd immunity really mean?

What is herd immunity?

According to the World Health Organization, herd immunity is the ‘indirect protection from an infectious disease that happens when a population is immune’. Immunity can be developed naturally when the body makes antibodies in response to a specific infection, which protect against future infections. Immunity can also be developed through vaccination, which triggers the immune system to identify and protect against future threats, without the risk of disease.

When a significant portion of a population becomes immune to an infectious disease, its spread can be greatly limited, protecting those in the community who are not immune or are at risk of serious infection.

The more transmissible (contagious) the disease is, the greater the proportion of the population that is immune is needed to limit the spread of the disease. The percentage of a population that needs to be immune in order to achieve herd immunity varies from disease to disease. This percentage typically ranges from 70%-90%.

Importance of herd immunity

Herd immunity can protect some of the most vulnerable people in the community, as some people cannot receive some vaccines or do not develop immunity to diseases. This vulnerable group of individuals can include newborns, the elderly and those whose immune systems are compromised due to illness or medications.  For these groups of individuals, herd immunity is a vital way of protecting them against life-threatening illness and disease.