Hjarðónæmi

Hjarðónæmi, also known as herd immunity or community immunity, is a form of indirect protection from an infectious disease that occurs when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity. When herd immunity is established, the spread of the disease from one person to another becomes unlikely because there are not enough susceptible people for the chain of transmission to continue.

The threshold for achieving herd immunity varies depending on the specific disease. Highly contagious diseases, such as measles, require a very high percentage of the population to be immune, often above 95%. Less contagious diseases may have a lower threshold. Immunity can be acquired through vaccination, which is a safe and effective way to build resistance without experiencing the illness itself, or through natural infection, though this carries the risk of severe illness, complications, and death.

Herd immunity is crucial for protecting vulnerable individuals who cannot be vaccinated, such as infants, the elderly, or those with compromised immune systems. By reducing the overall circulation of a pathogen, the risk of these individuals encountering and contracting the disease is significantly lowered. Maintaining high vaccination rates is essential for preserving herd immunity and preventing outbreaks of vaccine-preventable diseases.