Have you heard of “herd immunity”?
It’s relevant to the current debate about mandatory vaccinations for children. It basically means that everyone doesn’t have to be immunized to prevent an outbreak of a contagious disease—as long as a critical percentage is immunized.
Here’s how the National Institute of Allergy and Infectious Disease defines it: “When a critical portion of a community is immunized against a contagious disease, most members of the community are protected against that disease because there is little opportunity for an outbreak. Even those who are not eligible for certain vaccines—such as infants, pregnant women, or immuno-compromised individuals—get some protection because the spread of contagious disease is contained.”
Herd immunity (a.k.a. community immunity) is achieved if the percentage of a population that is immune (due to vaccination or having had the disease) is above a certain threshold. For measles, it’s estimated to be in the 83% to 94%.
However, there’s a catch. The threshold is even higher for schools or other places where people congregate for periods of time.
Recent outbreaks of measles and pertussis (whooping cough) have been attributed to lowered herd immunity caused by increasing numbers of parents who opt out of immunizations for their kids.
Herd immunity is about probabilities. If an unimmunized child comes into close contact with the one person who has an active case of measles, it doesn’t matter what percentage of the population is immune.
Did you know about herd immunity?
Do we have a civic duty to maintain herd immunity?
Or, should parents be able to opt out even if it raises the vulnerability of the community?
Should measles vaccination be mandatory for all young children?
Where should measles vaccination rank in health priorities?
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