Herd immunity: What it is and why it’s important
This article, written by Venkat Iyer, MD, originally appeared on Allina Health’s ‘Healthy Set Go’ website.
Measles, chickenpox and polio all have one thing that can stop them in their tracks–herd immunity. That’s when a large portion of a population becomes immune to a specific disease through vaccination or natural immunity, making it unlikely to spread. Read this article to learn how herd immunity works and why it’s important.
Immunity is your body’s ability to protect itself from disease. When a potentially harmful substance (antigens) enters the body, your immune system reacts by creating antibodies and special memory immune cells that protect you from getting or spreading the disease in the future.
How well and how long antibodies can protect you varies for each disease. Immunity to different diseases can last months, years or a lifetime.
How herd immunity works
When an infectious disease enters a community, and no one or just a few people are immune, it quickly spreads. Herd immunity can be accomplished when most of a population becomes immune. There are two methods for a community to reach herd immunity: vaccine immunity and natural infection.
Herd immunity and vaccines
Vaccination is the safest method for disease protection and reaching herd immunity. Vaccines expose your body to a weakened or killed form of the pathogen, triggering your immune system to identify and protect you from future threats.
The goal is to slow the spread of disease, build lasting immunity for everyone and protect vulnerable populations without risking lives.
Herd immunity without vaccine
Herd immunity can also be reached through natural infection, where a community allows an actual disease to spread. Natural infection infects a population until a disease runs out of people to infect. This obviously is not a recommended way to achieve herd immunity due to risk of loss of life. After recovering, your immune system’s antibodies are naturally developed to protect you from future infection.
The level of natural protection from antibodies varies because some people have a stronger immune response than others. The risks of natural infection are far greater than getting vaccinated. Building immunity through natural infection costs lives and strains health care systems.
Herd immunity barriers
Herd immunity can be complicated and there isn’t a one-size-fits-all approach to get there. There are several barriers to reaching herd immunity:
Herd immunity threshold. The threshold determines how many people in a population need immunity. According to the World Health Organization, the percentage of immune people needed to achieve herd immunity for each disease is different.
That’s because some infections are more contagious than others. For example, because measles is extremely contagious, 95% of the population needed the measles vaccine to accomplish herd immunity. The more people who get vaccinated, the more protection a community has.
Vaccine hesitancy. Vaccine hesitancy is the delayed acceptance or refusal of vaccines despite availability. Common reasons for reluctance include safety concerns, religious beliefs, misinformation and distrust stemming from the historical mistreatment of disadvantaged groups.
Disease variants. New variants of a virus evolve through mutations. When a disease-causing organism called a pathogen mutates and enters your body, it makes copies of itself to hitch a ride on more of your cells. The more cells a virus latches onto, the harder it is for your immune system to extinguish the threat. Some variants can make a virus more infectious and severe because a vaccine may only be effective for the original disease, while other mutations don’t pose additional threats.
Why herd immunity is important
Herd immunity can protect a population from a specific disease, even if a small part of a population isn’t immune–for example, children and those with a severely weakened immune system. Deciding to get vaccinated means protecting you and those who can’t protect themselves.
According to the Centers for Disease Control and Prevention (CDC), some should not get certain vaccines because of age, health conditions and other factors. Reaching the herd immunity threshold increases a community’s ability to contain a virus.
Herd immunity myths
The concept of herd immunity is widely misunderstood. Myths can spread like a virus and prolong a health crisis. That’s why it’s important to verify health information with the CDC before sharing it with others.
Myth: Vaccines create immediate herd immunity. Vaccines make it possible to decrease cases and slow the spread of a disease. However, immunity doesn’t happen right away, even when the threshold is reached.
Myth: I’m protected because I’m a part of the herd. Herd immunity doesn’t protect everyone who doesn’t get vaccinated. Deciding to refuse vaccination can leave you and others vulnerable to getting and spreading a disease, even if you have antibodies from a previous infection.
Myth: Antibodies provide lifelong protection. Antibodies don’t provide lifelong immunity for all viruses. That’s why yearly vaccinations are needed for some viruses like the flu.
Herd immunity and COVID-19
COVID-19 herd immunity could be challenging to reach in the near future as vaccination rates decrease and variants continue to spread. According to the Minnesota Department of Health, we don’t know enough about COVID-19 to confirm if herd immunity is possible.
What health experts do know is that high vaccine rates can decrease hospitalizations, contain the virus and slow the spread. Vaccinations can slow the spread by preventing you from getting the virus and reduce the risk of transmitting it to others. Schedule your COVID-19 vaccination today by calling 507-217-5011, or schedule with the Allina Health Account or online at www.allinahealth.org.