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Herd immunity and COVID-19 (coronavirus): What you need to know Understand what's known about herd immunity and what it means for coronavirus disease 2019 ( COVID-19 ).
Curious as to whether herd immunity against the coronavirus disease 2019 ( COVID-19 ) might slow the spread of the disease?
Understand how herd immunity works and what experts are saying about its potential impact on the COVID-19 pandemic.
Why is herd immunity important?
Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely.
As a result, the whole community becomes protected — not just those who are immune.
If the proportion of the population that is immune to the disease is greater than this threshold, the spread of the disease will decline.
This is known as the herd immunity threshold.
What percentage of a community needs to be immune in order to achieve herd immunity?
It's estimated that 94% of the population must be immune to interrupt the chain of transmission.
There are two paths to herd immunity for COVID-19 — vaccines and infection.
Vaccines A vaccine for the virus that causes COVID-19 is an ideal approach to achieving herd immunity.
Vaccines create immunity without causing illness or resulting complications.
Herd immunity makes it possible to protect the population from a disease, including those who can't be vaccinated, such as newborns or those who have compromised immune systems.
Using the concept of herd immunity, vaccines have successfully controlled deadly contagious diseases such as smallpox, polio, diphtheria, rubella and many others.
Reaching herd immunity through vaccination sometimes has drawbacks, though.
People who object to vaccines often live in the same neighborhoods or attend the same religious services or schools.
If the proportion of vaccinated people in a community falls below the herd immunity threshold, exposure to a contagious disease could result in the disease quickly spreading.
Measles has recently resurged in several parts of the world with relatively low vaccination rates, including the United States.
Opposition to vaccines can pose a real challenge to herd immunity.
Natural infection Herd immunity can also be reached when a sufficient number of people in the population have recovered from a disease and have developed antibodies against future infection.
During the 2009-10 flu season, H1N1 caused the respiratory infection in humans that was commonly referred to as swine flu.
However, there are some major problems with relying on community infection to create herd immunity to the virus that causes COVID-19 .
First, it isn't yet clear if infection with the COVID-19 virus makes a person immune to future infection.
Further research is needed to determine the protective effect of antibodies to the virus in those who have been infected.
Even if infection with the COVID-19 virus creates long-lasting immunity, a large number of people would have to become infected to reach the herd immunity threshold.
Experts estimate that in the U.S., 70% of the population — more than 200 million people — would have to recover from COVID-19 to halt the epidemic.