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How Can Herd Immunity Help Limit the Spread of COVID-19?

  • Category: Blog
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  • Written By: Dale Bratzler, DO, MPH
How Can Herd Immunity Help Limit the Spread of COVID-19?

Q: What does the term “herd immunity“ mean?

A: The virus that causes COVID-19 spreads easily from an infected person to other people who are still susceptible to the infection. However, when enough people become immune to the infection, whether through vaccination or previous infection, an infected person is less likely to encounter someone who is still susceptible to the infection. When enough people are immune to the disease, it can dramatically slow the spread of the virus. This concept is called “herd immunity.”

Q: How does herd immunity work to limit the spread?

A: A virus can only spread from someone who has the infection to someone who is still susceptible to the infection. The more people in the community who have immunity, it becomes less likely that an infected person will encounter someone to infect. The more contagious the virus is, then more people will need to be immune to stop the spread of the virus.

Q: What other pandemics has herd immunity helped to end?

A: We rely on herd immunity to slow the spread of many viral diseases. For example, measles is one of the most contagious viral infections that can cause severe disease in children. Most studies have shown that 93-95% of people need to be immune to the measles virus to slow the spread of the disease. So for many years, measles vaccination has been mandatory for school-aged children to get the entire population some immunity to the disease. When the majority of people have immunity to measles, the virus cannot spread.

Q: How do herd immunity and the vaccine work together?

A: Vaccination is the preferred way to develop immunity to an infection. It has been estimated that 80-85% of people (and perhaps higher) need to be immune to the virus that causes COVID-19 to slow its spread, so it is important to get the vaccine to as many people as possible. Achieving herd immunity by allowing the infection to spread is not acceptable. Up to 12% of people in Oklahoma who have a confirmed case of COVID-19 will end up in the hospital, and some will have severe complications of the disease. Vaccination is the much safer way to achieve herd immunity.

Q: How will we know when we have reached herd immunity?

A. Both by monitoring rates of immunity in the community (for instance, testing for antibodies), but most importantly, by observing a declining number of new cases in our state, suggesting decreased community spread of the virus.

Q: Is herd immunity a permanent fix?

A: Not necessarily. It is possible that the virus that causes COVID-19 could mutate and start spreading again even after herd immunity is achieved. But to date, mutations of the virus do not seem to be decreasing the effectiveness of the vaccines that have been developed.

Q: What else should the public know about herd immunity and the vaccine?

A: The health risks from COVID-19 infection are far greater than risks that may be related to the vaccine. Individuals should seek the vaccine when it is made available to them.

Dale Bratzler, DO, MPH ​​​​​​This article was written by one of our experts, Dale Bratzler, DO, MPH, to discuss the term "Herd Immunity" and how it works to limit the spread of COVID-19. For more information on COVID-19 and the available vaccines, please visit the OU Health COVID-19 site.