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Medical Advisory Team: Herd Immunity

Posted by on Jan 29, 2021


What is herd immunity?

Herd immunity occurs when a large percentage of a community (the herd) becomes immune to a contagious disease, thereby making the continued spread of the disease to susceptible persons unlikely. In other words, herd immunity protects the entire community from the disease, not just the folks who are immune. This is important because there are people in all communities who can’t be vaccinated, such as newborns or those who have compromised immune systems.


How many people must be immune to the COVID-19 virus for herd immunity to work?

Epidemiologists have determined that about 70% of the people within a community must be immune to SARS-CoV-2 to achieve herd immunity. Thus, it is more than twice as likely that an infected person who transmits the virus in such a community will pass it to someone who is already immune to the virus than to someone who is not. The immune person’s antibodies against the virus will then “neutralize” the virus and eliminate it as a source for furthering the spread of the disease.


How long does herd immunity to the COVID-19 virus last?

Herd immunity to the virus should remain in effect as long as at least about 70% of the community members are immune. What’s not yet clear, though, is how long each person’s immunity to this virus will last, whether from vaccination or actual infection. Stay tuned.


I have heard that people who have received the COVID vaccine may still carry and transmit the virus. Couldn’t they continue to infect and make immune anyone who hasn’t been vaccinated?

Sure, but please recall that the objective of vaccination is to stop the spread of the disease. When the number of people who are immune to the SARS-CoV-2 virus outnumbers by more than 2 to 1 those who are susceptible to infection by it, the rapid spread of the disease effectively stops. In the meantime, anyone who contracts and subsequently recovers from COVID-19 will join the ranks of the immune. The more, the merrier.

Tags: covid-19