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Herd immunity (also called herd effect, community immunity, population immunity, or mass immunity) is a form of indirect protection that applies only to contagious diseases.
If the proportion of the population that is immune exceeds the herd immunity level for the disease, then the disease can no longer persist in the population and its transmission dies out. [28] Thus, a disease can be eliminated from a population if enough individuals are immune due to either vaccination or recovery from prior exposure to disease.
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Strong herd immunity reduces this vulnerability. Increasing herd immunity during an outbreak or when there is a risk of an outbreak is perhaps the most widely accepted justification for mass vaccination. When a new vaccine is introduced, mass vaccination can help increase coverage rapidly. [43]
is the average number of people infected from one other person. For example, Ebola has an of two, so on average, a person who has Ebola will pass it on to two other people.. In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted (pronounced R nought or R zero), [1] of an infection is the ...
In epidemiology, force of infection (denoted ) is the rate at which susceptible individuals acquire an infectious disease. [1] Because it takes account of susceptibility it can be used to compare the rate of transmission between different groups of the population for the same infectious disease, or even between different infectious diseases.
For example, if individual A values their own immunity to an antigen at $100 but the immunization costs $150, individual A will decide against receiving immunization. However, if the added benefit of herd immunity means person B values person A's immunity at $70 then the total social marginal benefit of their immunization is $170.