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How can a population reach a state of herd immunity?

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There are two ways this can happen.

You can develop resistance naturally. When your body has exposure to a virus or bacteria, it makes antibodies to fight off the infection. When you recover, your body keeps these antibodies. Your body will defend against another infection.

Vaccines can also build resistance. They make your body think a virus or bacteria has infected it. You don’t get sick, but your immune system still makes antibodies. The next time your body meets that bacteria or virus, it’s ready to fight it off.

From: What Is Herd Immunity? WebMD Medical Reference

SOURCES:

CDC: “Vaccines and Immunizations: Glossary,” “Frequently Asked Questions -- Coronavirus Disease 2019 Basics,” “Understanding How Vaccines Work,” “Polio Elimination in the United States.”

Science Media Centre: “Expert Comments About Herd Immunity.”

Association for Professionals in Infection Control and Epidemiology: “Herd Immunity.”

John Hopkins Medicine: “The Immune System.”

mBio : “High Zika Virus Seroprevalence in Salvador, Northeastern Brazil Limits the Potential for Further Outbreaks.”

Centre for the Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine: “Critical Immunity Thresholds for Measles Elimination.”

Journal of Travel Medicine : “The reproductive number of COVID-19 is higher compared to SARS coronavirus.”

National Institutes of Health: “NIH clinical trial of investigational vaccine for COVID-19 begins.”

Imperial College London: “Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand.”

Journal of Medical Virology : “Coronavirus infections and immune responses.”

Reviewed by Arefa Cassoobhoy on March 23, 2020

SOURCES:

CDC: “Vaccines and Immunizations: Glossary,” “Frequently Asked Questions -- Coronavirus Disease 2019 Basics,” “Understanding How Vaccines Work,” “Polio Elimination in the United States.”

Science Media Centre: “Expert Comments About Herd Immunity.”

Association for Professionals in Infection Control and Epidemiology: “Herd Immunity.”

John Hopkins Medicine: “The Immune System.”

mBio : “High Zika Virus Seroprevalence in Salvador, Northeastern Brazil Limits the Potential for Further Outbreaks.”

Centre for the Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine: “Critical Immunity Thresholds for Measles Elimination.”

Journal of Travel Medicine : “The reproductive number of COVID-19 is higher compared to SARS coronavirus.”

National Institutes of Health: “NIH clinical trial of investigational vaccine for COVID-19 begins.”

Imperial College London: “Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand.”

Journal of Medical Virology : “Coronavirus infections and immune responses.”

Reviewed by Arefa Cassoobhoy on March 23, 2020

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