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Why is high vaccination coverage needed for herd immunity against measles?

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Health monitoring — human disease The routine monitoring of blood pressure levels is an important part of assessing an individual's health. Blood pressure provides information about the amount of blood in circulation and about heart function and thus is an important indicator of disease.

High vaccination coverage is essential for herd immunity against measles because the disease is exceptionally contagious.12

The contagiousness of an infectious disease is measured by its basic reproduction number, or $R_{0}$ , which represents the average number of people one infected individual will infect in a fully susceptible population. Measles has a very high $R_{0}$ value, ranging from 12 to 18. Because the virus spreads so easily—lingering in the air for up to two hours after an infected person coughs or sneezes—the proportion of the population that must be immune to prevent sustained spread is significantly higher than for less contagious diseases.12

To achieve the necessary threshold for herd immunity, typically 95 percent or more of the population must be vaccinated. When vaccination rates drop below this level, the density of susceptible individuals becomes high enough for the virus to spread rapidly through communities, leading to outbreaks. Maintaining high coverage is a critical public health responsibility to protect those who are vulnerable and to prevent the resurgence of this serious disease.231