Herd immunity occurs when a high percentage of a population is immune to a disease, preventing its spread. Vaccination policies aim to build community immunity, with thresholds varying depending on the disease. Regular boosters are important, and herd immunity has led to the eradication of smallpox and rare cases of polio and diphtheria. It is used to encourage vaccinations and protect society at large.
In immunology, herd immunity refers to a situation in which a high percentage of a population is immune to a disease, essentially nipping the disease in its tracks because it cannot find new hosts. You may also hear this concept referred to as “community immunity.” The threshold for herd immunity varies, depending on the disease, with more virulent agents requiring a higher percentage of the population to be vaccinated to create the desired immunity. In addition to being used in disease prevention, community immunity is also used to fight ongoing epidemics.
Most vaccination policies focus on building community immunity. Many countries require childhood vaccinations, for example, to protect children from common diseases and to ensure 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 the outbreak of disease by creating widespread immunity, but they are not always successful. Sometimes a disease mutates or is completely new, or a batch of vaccinations is faulty, or a large percentage of the population goes unvaccinated, creating a situation where an outbreak can occur, because so much of the population is vulnerable. In the event of an outbreak of a serious disease, agencies such as the World Health Organization (WHO) can send teams within days to figure out the cause of the outbreak and develop a vaccine, in hopes of building herd immunity to stop the outbreak. epidemic in its tracks.
For some diseases, immunity thresholds are as high 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. It’s also extremely important to get regular boosters, 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 nations with established vaccination policies.
The concept of herd immunity is often used to encourage reluctant parents to vaccinate their children. In addition to ensuring their children are protected from completely preventable diseases, childhood vaccinations also benefit society at large by creating widespread protection from disease. Similarly, adults may be reminded to get boosters to help protect their communities.
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