The Unforgiving Math That Stops Epidemics | Quanta Magazine

The Unforgiving Math That Stops Epidemics | Quanta Magazine:
"As the annual flu season approaches, medical professionals are again encouraging people to get flu shots.
Perhaps you are among those who rationalize skipping the shot on the grounds that “I never get the flu” or “if I get sick, I get sick” or “I’m healthy, so I’ll get over it.”
What you might not realize is that these vaccination campaigns for flu and other diseases are about much more than your health.
They’re about achieving a collective resistance to disease that goes beyond individual well-being — and that is governed by mathematical principles unforgiving of unwise individual choices.
When talking about vaccination and disease control, health authorities often invoke “herd immunity.” 
This term refers to the level of immunity in a population that’s needed to prevent an outbreak from happening. 
Low levels of herd immunity are often associated with epidemics, such as the measles outbreak in 2014-2015 that was traced to exposures at Disneyland in California.
A study investigating cases from that outbreak demonstrated that measles vaccination rates in the exposed population may have been as low as 50 percent.
This number was far below the threshold needed for herd immunity to measles, and it put the population at risk of disease..."
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