As more Americans get vaccinated against COVID-19, there has been increasing discussion of reaching herd immunity. What is herd immunity, why is it important, and how close are we to reaching it? This resource provides an overview of some of the various factors surrounding herd immunity and COVID-19.
According to the Mayo Clinic, herd immunity is reached when a sufficiently large percentage of a population becomes immune to a certain disease—in this case, COVID-19. Once herd immunity is reached, the virus has trouble spreading between individuals, which means infection rates drastically decline and the entire “herd” becomes immune to the disease.
To reach herd immunity, the herd immunity threshold must be crossed, which refers to the percentage of a population that is required to be immune to a certain virus/pathogen, whether that be from infection and/or vaccination. However, there are differing opinions as to what this threshold is for COVID-19.
“It’s still unclear exactly how many people will need to be vaccinated in order to achieve herd immunity to COVID-19, but experts estimate that it will take somewhere around 70% of the population — with some estimates ranging as high as 90%,” said Dr. Ashley Drews, a specialist in Infectious Diseases at Houston Methodist Hospital, during an interview.
Generally, it’s safe to say that the majority of the population will need to gain COVID-19 immunity via infection or immunization in order to reach herd immunity. As mentioned in the ‘herd immunity threshold’ link above, when it comes to herd immunity, individuals can gain immunity in two ways: through natural immunity (i.e. infections) or vaccines (passive immunity).
Natural (active) immunity can be acquired following an infection of a certain pathogen (i.e. bacteria, viruses, et cetera). Following this initial infection, your body then creates antibody cells that “remember” how to fight the pathogen should your body encounter it again in the future. For a more in-depth explanation of how natural immunity works, view this comprehensive resource from the CDC.
Relying on natural immunity to reach herd immunity is generally seen as less than ideal for two reasons.
Natural immunity requires each individual to recover from the potentially severe side-effects of COVID-19.
Through vaccination, your body learns how to fight an infection without actually getting sick from the pathogen itself. Therefore, following a vaccination, if you were to be exposed to that pathogen, such as COVID-19, your immune system would have instructions on how to fight the virus and help protect your body from disease. For a more in-depth explanation of how immunity through vaccines works, view this comprehensive resource from the CDC.
Relying on vaccines to reach herd immunity is generally recommended rather than solely relying on natural immunity for the following reasons:
Although some individuals experience side effects from COVID-19 vaccines, according to the CDC, the side effects are generally mild.
We are able to track how many people have received COVID-19 vaccines and when they have received them, meaning we can make more intelligent assessments regarding if herd immunity has been reached.
Determining how close we are to reaching herd immunity through vaccines is difficult because of the differences in opinion regarding the percentage of the population that needs to gain immunity to COVID-19 in order to reach herd immunity.
As of May 30, more than 134 million Americans are fully vaccinated against COVID-19. More than 165 million have received at least one dose of a vaccine that requires two doses. That means about 40% of Americans are fully vaccinated and about 50% have received at least one dose.
According to this data, herd immunity is inching closer—but even if we make the assumption that only 70% of the population will need to be immune to COVID-19 to reach herd immunity, we’re not there quite yet.
The number of Americans receiving COVID-19 vaccinations is decreasing daily. Coupled with vaccine hesitancy from a certain portion of the population and the fact that limited vaccination options are currently available for minors, in a few months, we may reach a situation where we are very close to herd immunity as a population, but still not quite there.
Even if we don’t reach herd immunity, we will still likely see a return to normalcy sometime in the near future. Certain vaccines have been shown to provide substantial protection against COVID-19, meaning vaccinated individuals will likely be able to live their lives with minimal restrictions.
“I think the more likely scenario is that [COVID-19] never completely goes away. The question is whether the risks become more like coronaviruses normally,” Dr. Eili Klein, Associate Professor of Emergency Medicine at Johns Hopkins University, said during an interview.
Some experts have weighed in on how the effects of COVID-19 might be less severe in the future. “We don’t typically cancel concerts and wear masks for the flu every year. It becomes a risk where the benefits of not doing all of this stuff outweigh the risks of it,” Dr. Klein said.
Due to ongoing vaccination efforts across the country, we’re closer to reaching herd immunity than we were a few months ago, but how far we have to go until we conclusively reach herd immunity remains to be seen.
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