Community immunity

Community Immunity also known as herd immunity, is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby providing a measure of protection for individuals who are not immune.

Overview

In a population where a large number of individuals are immune, chains of infection are likely to be disrupted, which stops or slows the spread of disease. The greater the proportion of individuals in a community who are immune, the smaller the probability that those who are not immune will come into contact with an infectious individual.

Mechanism

Immunity against infectious diseases is a complex process that involves many components of the immune system. For many diseases, it is often associated with the presence of antibodies against the disease in a person's system. Antibodies are produced by the body in response to infection or vaccination.

When a large percentage of the population is vaccinated, it is difficult for the disease to spread because there are so few susceptible people left to infect. This can effectively stop the spread of disease in the community. It is particularly crucial for protecting people who cannot be vaccinated. These include children who are too young to be vaccinated, people with immune system problems, and those who are too ill to receive vaccines (such as some cancer patients).

Importance

The concept of community immunity is crucial in controlling the spread of contagious diseases. Mass vaccination campaigns aim at creating community immunity. For example, the measles vaccine has a community immunity threshold of about 95%. This means that 95% of the population must be vaccinated to prevent outbreaks.

Community immunity is also important in protecting those who cannot safely receive vaccines, like patients with an allergy to a vaccine component, those with weakened or failing immune systems (such as HIV/AIDS patients, or cancer patients undergoing chemotherapy), and the elderly.

Challenges

Community immunity relies on the cooperation of the majority of the community to be effective. Vaccine hesitancy, the reluctance or refusal to vaccinate, poses a risk to community immunity by reducing the overall level of immunity in the population and increasing the chances of outbreak of diseases.

See also

• Vaccination
• Infectious disease
• Immunity
• Vaccine hesitancy