What Is Herd Immunity and Why It’s Essential for Preventing Measles
When it comes to protecting communities from infectious diseases like measles, one concept plays a powerful role: herd immunity. You may have heard this term during discussions about vaccines, but what does it really mean—and why is it so important?
What Is Herd Immunity?
Herd immunity (also known as community immunity) occurs when a high enough percentage of the population is immune to a disease—either through vaccination or previous infection—making it difficult for the disease to spread. This not only protects those who are immune but also those who cannot be vaccinated, such as:
- Infants too young for vaccines
- Individuals with weakened immune systems
- People with certain medical conditions
When a population reaches herd immunity, outbreaks become rare, and even those at higher risk are shielded from infection.
Why Is Herd Immunity Critical for Measles?
Measles is one of the most contagious viruses known. It spreads through the air when an infected person coughs or sneezes, and the virus can linger in the air or on surfaces for up to two hours. A person with measles can infect up to 90% of people nearby who are not immune (Centers for Disease Control and Prevention [CDC], 2023).
Because measles spreads so easily, it requires a very high level of community immunity to prevent outbreaks. Experts estimate that about 95% of the population needs to be immune to stop measles transmission (World Health Organization [WHO], 2023).
How Do Vaccines Help Achieve Herd Immunity?
The measles, mumps, and rubella (MMR) vaccine is the most effective tool we have for preventing measles. Two doses of the MMR vaccine are about 97% effective at preventing measles (CDC, 2023).
When most people in a community are vaccinated, the virus cannot spread easily—even if a case is introduced by travel or contact with an unvaccinated person. This prevents outbreaks and protects those who rely on herd immunity to stay safe.
What Happens When Vaccination Rates Drop?
In recent years, some communities have experienced a decline in vaccination coverage due to misinformation, access issues, or vaccine hesitancy. Unfortunately, this can lead to measles outbreaks, even in countries where the disease was previously eliminated.
For example, the United States declared measles eliminated in 2000, but in 2019, over 1,200 cases were reported—the highest number in nearly three decades—due to pockets of low vaccination coverage (CDC, 2023).
Globally, measles deaths increased by 43% between 2021 and 2022, largely due to decreased vaccine coverage during the COVID-19 pandemic (WHO & CDC, 2023).
Key Takeaway: Community Protection Starts with You
Getting vaccinated is not just about individual protection—it’s about protecting your community. By keeping MMR vaccination rates high, we can prevent the return of a disease that is both dangerous and entirely preventable.
Even if you’re healthy, your immunity helps protect those who cannot be vaccinated and contributes to a safer, healthier community for everyone.
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You can also visit the links below for more information on childhood vaccines and when your child should receive certain immunizations.
References
- Centers for Disease Control and Prevention (CDC). (2023). Measles (Rubeola). https://www.cdc.gov/measles/index.html
- Centers for Disease Control and Prevention (CDC). (2023). Measles Vaccination. https://www.cdc.gov/vaccines/vpd/measles/index.html
- World Health Organization (WHO). (2023). Measles. https://www.who.int/news-room/fact-sheets/detail/measles
- World Health Organization (WHO) & Centers for Disease Control and Prevention (CDC). (2023). Measles and rubella surveillance data. https://www.cdc.gov/measles/global.html
