In immunology, herd immunity refers to a situation where a high percentage of a population is immune to a disease, essentially stopping the disease because it cannot find new hosts. You may also hear this concept called "community immunity." The threshold for herd immunity varies, depending on the disease, with more virulent agents requiring vaccination of a higher percentage of the population to create the desired immunity. In addition to being used in disease prevention, herd immunity is also used to combat ongoing outbreaks.
Most vaccination policies focus on creating herd immunity. Many countries require childhood vaccinations, for example, protecting children from common diseases and ensuring that when these diseases enter the population, they cannot prey on children or adults who have been previously vaccinated or exposed to the disease. Building herd immunity is especially important in crowded environments that facilitate the spread of disease, such as schools.
Immunologists try to prevent disease outbreaks by creating widespread immunity, but they are not always successful. Sometimes a disease mutates or is entirely new, or a batch of vaccine is defective, or a large percentage of the population is not vaccinated, creating a situation where an outbreak can occur, because much of the population is vulnerable. In the event of a serious disease outbreak, agencies like the World Health Organization (WHO) can dispatch teams in a matter of days to discover the cause of the outbreak and develop a vaccine, hoping to create herd immunity to stop the spread. sprout in their tracks
For some diseases, immunity thresholds are as low as 50%, especially when combined with good hygiene. In other cases, up to 90% of the population may need to be vaccinated to create the desired protection. Getting regular boosters is also extremely important, as some vaccines lose their effectiveness over time, leaving people vulnerable to an outbreak. Herd immunity led to the eradication of smallpox, and explains why diseases such as polio and diphtheria are rare in developed countries with established vaccination policies.
The concept of herd immunity is often used to encourage reluctant parents to vaccinate their children. In addition to ensuring that your children are protected from entirely preventable diseases, childhood immunizations also benefit society at large by creating widespread protection against disease. Similarly, adults can be reminded to get reinforcements to help protect their communities.