What is herd immunity?

By: Hayat Osman

Herd immunity is when enough people in a population are immune to a disease that it slows down the spread of the illness.

When a disease such as COVID-19 begins to spread scientists start by looking at the reproduction number, this represents how many people in a susceptible population could catch the virus from a single infected person.

For example, with the measles, one infected person on average would pass the virus to 12-18 other people. With COVID-19, an infected person would likely infect 2-4 other people, furthering the spread of the disease.

When people in a population start becoming immune to a disease, the chances of infecting others goes down making it harder for the virus to spread. The result is the community being protected against diseases as well as those with weak immune systems.

Scientists say herd immunity could be reached two ways: through broad infection or vaccination. To get herd immunity through broad infection the majority of a population would need to get sick from the virus and develop natural defenses such as antibodies to fight the disease.

But this method would be deadly because less than 5% of people worldwide have had COVID-19 and to reach immunity that number would need to be between 60-70%.

Experts say the most efficient way to herd immunity is through vaccination.

Vaccines help produce antibodies which help the immune system recognize diseases, controlling it from further spread. The benefits of reaching herd immunity through vaccination is only having the needed amount of people vaccinated, while broad infection may affect 100% of the population and generations after.

With COVID-19 the number of vaccinations that would be necessary to reach immunity is between 60-70%.

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