COVID-19 Vaccine Key to Reaching ‘Herd Immunity’

Photo illustration of mask with people

Now that there are several promising vaccines for COVID-19 nearing approval, the country is on a path to so-called herd immunity.

Here’s what you need to know:

What is herd immunity?

Herd immunity, or community immunity, happens when a sufficient proportion of a population (the percentage varies by disease) is immune to an infectious disease through vaccination or prior illness to make its spread from person to person unlikely, according to the Centers for Disease Control and Prevention.

Even individuals not vaccinated (such as newborns and those with contraindications for the vaccines) are offered some protection because the disease has little opportunity to spread within the community.

This assumes that COVID-19 immunity through infection is long-lasting, said Christelle Ilboudo, MD, infectious disease expert at MU Health Care. Some studies have shown a progressive decline in antibodies after infection with other types of coronaviruses, but scientists are still not certain whether infection provides long-term protection from the virus.

What is an example of herd immunity?

Measles provides a good example. It is a highly contagious infectious disease for which we have very effective vaccines. Public health experts say if 93-95% of the population is immune to measles, a feasible target with the available vaccine, then that will protect the entire population.

This herd or community immunity acts as a barrier against the disease, with the immune people breaking the potential chain of transmission so those vulnerable populations are unlikely to get it.

How close are we to herd immunity for COVID-19?

Experts estimate that herd immunity would require around 80-90% of the population to have COVID-19 immunity, either through prior infection or vaccination. That's why experts are encouraging the public to get the COVID-19 vaccine.

“We have not achieved any herd immunity through a natural disease process to most major infectious diseases that affect the population to this scale,” she said. “All of the major infections I know of have required vaccination.”

Until a vaccine is widely available, the best course of action is to continue following public health measures — physical distancing, masking in public and good hand-washing hygiene — as those also break the virus transmission chain.

Once a vaccine is widely available, experts encourage vaccination as the next step on the path to herd immunity.

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