Fact Check: Measles has an R number of 12 to 18, meaning one infected person can spread it to up to 18 others in an unvaccinated population.

Fact Check: "Measles has an R number of 12 to 18, meaning one infected person can spread it to up to 18 others in an unvaccinated population."

What We Know

The basic reproduction number, commonly referred to as R0, is a crucial metric in epidemiology that indicates the average number of secondary infections produced by one infected individual in a completely susceptible population. For measles, the R0 is widely accepted to be between 12 and 18. This means that one person infected with measles can potentially infect anywhere from 12 to 18 other individuals if they are all unvaccinated and susceptible to the virus (Guerra et al., 2017).

Measles is recognized as one of the most contagious infectious diseases, primarily due to its transmission through respiratory droplets and its ability to remain airborne for extended periods (WHO). In 2022, measles was responsible for approximately 136,000 deaths globally, predominantly affecting unvaccinated populations (Tranter et al., 2024).

Analysis

The claim that measles has an R number of 12 to 18 is supported by multiple credible sources. The systematic review conducted by Guerra et al. (2017) provides a comprehensive analysis of R0 estimates for measles, confirming the commonly cited range of 12-18. This range is consistent across various studies, highlighting the disease's high infectivity in populations lacking immunity (Guerra et al., 2017).

Additionally, the CDC and WHO corroborate this information, emphasizing measles' high transmission rates and the critical need for vaccination to prevent outbreaks (CDC, WHO). The reliability of these sources is high, as they are established public health organizations with extensive expertise in infectious diseases.

However, it is important to note that while the R0 provides a general estimate, actual transmission can vary based on factors such as population density, vaccination coverage, and public health interventions. For instance, during outbreaks, the effective reproduction number may differ from the theoretical R0 due to varying levels of immunity in the population (Tranter et al., 2024).

Conclusion

The claim that "measles has an R number of 12 to 18, meaning one infected person can spread it to up to 18 others in an unvaccinated population" is True. This assertion is backed by substantial epidemiological evidence and is consistently supported by reputable health organizations. The high R0 of measles underscores the importance of vaccination in controlling its spread and preventing outbreaks.

Sources

1. The basic reproduction number (R 0 ) of measles
2. Onward Virus Transmission after Measles Secondary ...
3. Measles Cases and Outbreaks
4. Measles Update — United States, January 1–April 17, 2025
5. What to Know About Measles and Vaccines | Johns Hopkins
6. Measles - World Health Organization (WHO)
7. Measles - World Health Organization (WHO)
8. Measles and rubella - World Health Organization (WHO)