Feature Article: If Vaccines Work, Why Do Unvaccinated People Pose a Risk?

Some people ask the question, “If vaccines work, why do unvaccinated people present a risk to those who have been vaccinated?” Two simple facts contribute to this answer. First: Vaccines aren’t 100 percent effective. So even some people who are vaccinated will still be at risk. Second: The greater the number of unvaccinated people in a community, the more opportunity germs have to spread. This means outbreaks are more difficult to stem and everyone is at greater risk of exposure — including vaccinated people.

This latter concept is known as community immunity, or more commonly, herd immunity. Each member of the community contributes to the collective health of the community because the way a pathogen survives is by finding new people to infect. The fewer susceptible people in a community, the less opportunity the pathogen has to spread.

Interestingly, people often do not think about the fact that there are times when every family needs the protection of their community. New babies and infants may be too young to be vaccinated, and older adults or adults being treated for illnesses may be more susceptible to infections as well.

To read more about community immunity and to find considerations for both vaccinated and unvaccinated family members, review the Vaccine Education Center’s newest “Special Topics Q&A” sheet Vaccinated or Unvaccinated: What You Should Know.

Additional resources

• Q&A: Infectious Diseases and Immune-compromised People
• Q&A: Infectious Diseases and Cancer Patients
• Webpage: Vaccine Science — What is Herd Immunity?

For more information on vaccines and the diseases they prevent, visit the Vaccine Education Center website.