COVID-19 science: Understanding the basics of ‘herd immunity’ – AHA

Dr. Eduardo Sanchez is the American Heart Association’s chief medical officer for prevention and a former state health commissioner of Texas. He has dealt with major public health crises – including the SARS outbreak. In this occasional series, he’ll break down various topics related to the coronavirus pandemic.

Recently I heard a medical “expert” on the news incorrectly define the term “herd immunity.” It’s a new phrase for many people, but we’re hearing about it more and more, so it’s important to understand exactly what it is.

people cheering

Photo by David Morris on

First, let’s discuss how immunity works for individuals. A person can become immune (or resistant) after exposure to a disease-causing agent, such as the coronavirus causing COVID-19 in this case. The process of becoming immune includes the production of antibodies specific to the virus for future protection.

This production typically happens when a person develops the symptoms of the viral disease, but also may occur without symptoms. Irrespective of the symptoms, after significant exposure and time to develop the antibodies, a person becomes immune to that specific virus. In other words, the person is naturally “protected.”

If a large group of people – the herd – is immune to a virus, then an individual in the middle of this group is unlikely to become infected. The virus has a very hard time getting through the herd. Herd immunity, then, happens when people in a community are protected from a virus and its associated disease to a degree that people who are not immune are still protected because of the high population immunity.

Herd immunity can slow the spread of a contagious virus. Herd immunity can be alternatively achieved by vaccinating people if there is an available vaccine (or vaccines). Treatments that may be discovered and developed will help prevent progression of disease, help people recover from COVID-19 and will probably add to herd immunity.

Herd immunity is disease-specific and is influenced by the ease with which the disease spreads from person to person, or the level of contagiousness. The specifics about coronavirus and herd immunity are not yet characterized. Regardless of the specifics, achieving herd immunity by the repeated process of infection of one person, recovery and immunity will take a long time – many, many months or even years.

It will take a long time to achieve worldwide herd immunity. It may take less time in some cities or countries, but it will take time. Those individuals who are immune will be able to get back to work and be protected from reinfection and, probably, not transmit the virus or disease.


Filed under coronavirus, coronavirus risk, COVID-19, herd immunity, immunity

5 responses to “COVID-19 science: Understanding the basics of ‘herd immunity’ – AHA

  1. Myra F Burton

    You are always a light of knowledge on so many different subjects! Thank you!

    Liked by 1 person

  2. garrystafford

    Hey Tony, always appreciate your research and informative articles. That’s why I’m writing this to you. I think it would be interesting to hear a little bit more of your perspective. How you’re handling this and what you do to be as protected as possible. And then on a more global scale if there might be anything positive or hopeful regarding dealing with the virus and or medications such as antivirals or for regulating symptoms, essentially bringing hope and positivity to the situation. That, of course, implies that there are some. And I think there are as many people are undoubtedly working on this across the globe. And perhaps this could be ongoing….

    Liked by 1 person

    • Thanks for your kind words, Garry, but I think that is beyond my pay grade. I am as in the dark as you and the next guy. Just try to keep my hands washed and not stand too close to anyone and hope this thing goes away.


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