02/17/2026
A series.
Antivaxxer: “It is the vaccinated shedding their live virus from the vaccine for a month after injection. They are causing outbreaks.”
Facts:
This claim is incorrect. Measles outbreaks are not caused by vaccinated individuals shedding vaccine virus. A systematic review of 773 articles found no evidence of human-to-human transmission of measles vaccine virus among thousands of genotyped clinical samples worldwide.[1] Measles outbreaks are driven by unvaccinated individuals, not vaccine recipients.[2][3][4]
While vaccine virus RNA can be detected in the respiratory tract of recently vaccinated individuals (typically 7-21 days post-vaccination), there is no evidence this leads to transmission. Studies in both children and macaques detected vaccine virus RNA but found no transmission to unvaccinated contacts.[5] When PCR testing detects measles in recently vaccinated individuals, it represents vaccine virus detection, not wild-type measles that can spread.[6][7]
The epidemiologic evidence clearly demonstrates that unvaccinated individuals drive measles transmission. Analysis of U.S. measles cases from 2001-2016 showed that among imported cases, 87% were unvaccinated or had unknown vaccination status.[2] During the 2019 U.S. outbreaks, an important contributing factor was misinformation about vaccine safety in underimmunized communities.[2] More recently, 96% of measles cases in the U.S. through May 2025 involved persons who were unvaccinated or had unknown vaccination status.[3]
Vaccinated individuals who develop breakthrough measles infections are 3-4 times less infectious than unvaccinated cases. The reproduction number (R) for vaccinated cases is approximately 0.10 compared to higher values for unvaccinated individuals.[8] Studies from outbreak settings confirm that vaccinated cases have significantly lower odds of onward transmission (OR 0.41-0.44) compared to unvaccinated cases.[9] In a Japanese workplace outbreak, no onward transmission from vaccinated cases was documented.[10]
The evidence is unambiguous: vaccine refusal, not vaccination, is associated with measles outbreaks. Unvaccinated children with exemptions are 22-35 times more likely to contract measles than vaccinated children, and among recent U.S. measles cases with known reasons for non-vaccination, 70.6% had nonmedical exemptions.[4]
References
1. A Systematic Review of Human-to-Human Transmission of Measles Vaccine Virus. Greenwood KP, Hafiz R, Ware RS, Lambert SB. Vaccine. 2016;34(23):2531-6. doi:10.1016/j.vaccine.2016.03.092.
2. Measles. Strebel PM, Orenstein WA. The New England Journal of Medicine. 2019;381(4):349-357. doi:10.1056/NEJMcp1905181.
3. Measles 2025. Do LAH, Mulholland K. The New England Journal of Medicine. 2025;393(24):2447-2458. doi:10.1056/NEJMra2504516.
4. Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis. Phadke VK, Bednarczyk RA, Salmon DA, Omer SB. JAMA. 2016;315(11):1149-58. doi:10.1001/jama.2016.1353.
5. Detection of Live Attenuated Measles Virus in the Respiratory Tract Following Subcutaneous Measles-Mumps-Rubella Vaccination. Watkins TA, Brockhurst JK, Germain G, Griffin DE, Foxman EF. The Journal of Infectious Diseases. 2025;231(4):1089-1093. doi:10.1093/infdis/jiae537.
6. Implications of Measles Inclusion by Commercial Syndromic Polymerase Chain Reaction Panels - United States, May 2022-April 2023. Thomas CM, Hartley A, Schmitz A, et al. MMWR. Morbidity and Mortality Weekly Report. 2024;73(12):260-264. doi:10.15585/mmwr.mm7312a3.
7. Shedding of Measles Vaccine RNA in Children After Receiving Measles, Mumps and Rubella Vaccination. Washam MC, Leber AL, Oyeniran SJ, Everhart K, Wang H. Journal of Clinical Virology : The Official Publication of the Pan American Society for Clinical Virology. 2024;173:105696. doi:10.1016/j.jcv.2024.105696.
8. Factors Associated With Measles Transmission in the United States During the Postelimination Era. Gastañaduy PA, Funk S, Lopman BA, et al. JAMA Pediatrics. 2020;174(1):56-62. doi:10.1001/jamapediatrics.2019.4357.
9. Onward Transmission of Measles Virus Among Vaccinated Cases in a Large Community Outbreak in Auckland, New Zealand, 2019. Evans I, Jury S, Morrison A, et al. Vaccine. 2024;42(23):126257. doi:10.1016/j.vaccine.2024.126257.
10. Epidemiology of a Workplace Measles Outbreak Dominated by Modified Measles Cases at Kansai International Airport, Japan, During August-September 2016. Kobayashi A, Shimada T, Tanaka-Taya K, et al. Vaccine. 2020;38(32):4996-5001. doi:10.1016/j.vaccine.2020.05.067.
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