What is herd immunity?
When most of a population is immune to an infectious disease, this provides indirect protection—or herd immunity (also called herd protection)—to those who are not immune to the disease.
When most of a population is immune to an infectious disease, this provides indirect protection—or herd immunity (also called herd protection)—to those who are not immune to the disease.
For example, if 80% of a population is immune to a virus, four out of every five people who encounter someone with the disease won’t get sick (and won’t spread the disease any further).
In this way, the spread of infectious diseases is kept under control. Depending how contagious an infection is, usually 70% to 90% of a population needs immunity to achieve herd immunity.
For infections without a vaccine, even if many adults have developed immunity because of prior infection, the disease can still circulate among children and can still infect those with weakened immune systems.
As with any other infection, there are two ways to achieve herd immunity: A large proportion of the population either gets infected or gets a protective vaccine.
If SARS-CoV-2, the virus that causes COVID-19, is like other coronaviruses that currently infect humans, we can expect that people who get infected will be immune for months to years, but probably not their entire lives.
Why is getting infected with SARS-CoV-2 to “get it over with” not a good idea? people sometimes exposed themselves intentionally as a way of achieving immunity.
For less severe diseases, this approach might be reasonable. But the situation for SARS-CoV-2 is very different: COVID-19 carries a much higher risk of severe disease and even death.
Source @JohnsHopkinsSPH @JohnsHopkins
Source @JohnsHopkinsSPH @JohnsHopkins
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