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R0 Measles Outbreak
About R0 Measles Outbreak
Measles has the highest R0 of any infectious disease at 12 to 18, meaning one case can infect up to 18 susceptible people. This extreme contagiousness makes measles the first disease to return when vaccination coverage drops. Measles was eliminated from the US in 2000, meaning no continuous transmission for over 12 months. However, imported cases cause outbreaks when they reach under vaccinated communities. In 2019, the US had 1,274 measles cases, the largest number since 1992, a total exceeded in 2025 amid a large outbreak centred in Texas. A 2014 to 2015 outbreak linked to Disneyland in California affected 147 people. Samoa experienced a devastating measles outbreak in 2019 with over 5,700 cases and 83 deaths in a population of approximately 200,000. The Samoan outbreak was linked to declining vaccination rates after two infants died in 2018 when MMR vaccine was incorrectly prepared with a muscle relaxant, which damaged public confidence. Global measles cases increased approximately 79 percent in 2023 compared to 2022, reflecting backsliding in vaccination coverage.
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