What Is Herd Immunity and How Does It Work? | Get Healthy Stay Healthy

What Is Herd Immunity and How Does It Work?

Published on Oct 01, 2020
Authored by Pfizer Medical Team

Herd immunity has been a popular topic of discussion in recent months due to the global spread of COVID-19. 

What is herd immunity?

Herd immunity occurs when the majority of a population is immune to a disease or virus.Otherwise known as community immunity1, it helps to slow the spread of infectious diseases in two ways:2

  1. People contract the disease and develop an immune response.

  2. People are vaccinated.

When enough people are vaccinated, everyone—including those who are too young or too sick to be immunised—receives some protection from the spread of diseases. An infectious disease is less likely to spread from person to person because there are fewer germs around to infect others. And if a person does get sick, the likelihood of an outbreak is low because more people are immune. 

When is herd immunity most effective? 

Scientists estimate that in order for herd immunity to be effective, about 70 - 90 percent3 of a population need to be immune to a disease, either by contracting the disease and recovering or getting a protective vaccine. This reaches what the World Health Organization (WHO) calls the herd immunity threshold.4

Although, there are factors to consider. For instance, if a disease is considered highly contagious, a higher percentage of immunity is needed. Measles, an extremely contagious disease that is preventable through vaccination, needs 93-95 percent4 of a population to be immune in order to reach herd immunity threshold and for measles to be eliminated.

Herd immunity works best when there is a vaccine to provide protection. For example, diseases like polio and smallpox5 were once very common, however due to widespread vaccination, these diseases have become extremely rare. The vaccines for these diseases have helped establish herd immunity.

Will herd immunity work for the Current Pandemic

There is currently no vaccine for COVID-19, and herd immunity has not yet been achieved for the novel coronavirus. It is still unclear whether herd immunity will work for COVID-19, partly due to the severity of the disease in some people, with data suggesting7 that COVID-19 carries a death rate that is higher than the flu. It is especially dangerous for more vulnerable individuals like the elderly and those with weakened immune systems.

There is still much to be learned about this new virus. Experts are determining whether building up an immune response will prevent reinfection from COVID-19, but more research8 is needed. Scientists around the globe are working tirelessly to develop a vaccine that will offer protection.

In the meantime, medical experts still strongly recommend practicing the necessary safety precautions which include:

  1. Wash your hands often and for at least 20 seconds.

  2. Practice safe physical distancing as recommended by local health authorities.

  3. Stay at home if you feel sick and get tested.

  4. If you are an older adult or have a compromised immune system or underlying medical conditions, check with your doctor if you are up to date with your vaccinations.

As the situation evolves quickly, up to date recommendations on protective measures are available from the Department of Health (Australia) and the Ministry of Health (New Zealand).