By Jointra Editorial Team, Certified EMT
When most people think about vaccines, they think about protecting themselves. But vaccines serve a second, equally critical function: they protect people who cannot be vaccinated — newborns, immunocompromised individuals, and those for whom vaccines are medically contraindicated. This population-level protection is called herd immunity, or community immunity.
When a sufficient proportion of a population is immune to a disease, the pathogen has difficulty finding new hosts. Each infected person transmits the disease to fewer people — eventually, transmission chains break before they can spread widely.
The threshold for herd immunity depends on the pathogen's basic reproduction number (R0) — how many people one infected person would infect in a fully susceptible population.
| Disease | R0 | Herd Immunity Threshold | |---|---|---| | Measles | 12–18 | 92–95% | | Mumps | 4–7 | 75–86% | | Polio | 5–7 | 80–86% | | Smallpox | 5–7 | 80–86% | | COVID-19 (original) | 2–3 | 50–67% | | COVID-19 (Omicron) | 8–15 | 88–93% |
Measles is so contagious that nearly 95% of the population must be immune before community protection is achieved.
When vaccination rates drop below the herd immunity threshold, outbreaks occur — not just among the unvaccinated, but among those who cannot be vaccinated. This is why measles outbreaks in the United States still happen: they occur in under-vaccinated communities and inevitably affect infants too young to be fully vaccinated and immunocompromised individuals.
Efficacy is measured in clinical trials under controlled conditions. Effectiveness is measured in real-world use, where storage conditions, variant evolution, and timing of vaccination all affect performance.
A vaccine with 90% efficacy reduces the risk of infection by 90% in clinical trials. Effectiveness in the real world may be slightly higher or lower depending on circulating strains and population factors.
EMS providers interact with high-risk patients — the elderly, the immunocompromised, the chronically ill. They also interact with the public during calls in ways that create transmission risk. EMS vaccination rates matter for workforce continuity, patient safety, and community health.
Many states now require certain vaccinations for EMS licensure. Influenza and hepatitis B vaccinations are among the most commonly required or strongly recommended.