A peer-reviewed systematic review published in Expert Review of Vaccines on Aug. 14, 2026, reported that vaccinated people who contract measles can pass it to others, according to the study’s authors. The review, which pooled data from 33 outbreak investigations across 18 countries, found that 70 of 890 vaccinated measles cases (7.9%) transmitted the virus to others, resulting in 237 direct secondary cases and 812 total downstream cases.
According to the study, nearly one-third of the transmitters (22 of 70) had received two or more doses of the measles-mumps-rubella (MMR) vaccine, a status often described as fully vaccinated. The review was authored by officials from the U.S. Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), Johns Hopkins University, and other public health institutions, according to the report.
Study Authors and Methodology
The study’s authors include officials who have held senior positions at major public health bodies, according to the paper. Walter Orenstein, former director of the U.S. Immunization Program, is a co-author, as is Paul Rota, who serves as the CDC’s measles laboratory chief. The author list also includes William Moss of Johns Hopkins University and Natasha Crowcroft, who served as the WHO’s senior technical adviser for measles and rubella and now holds a position with the Public Health Agency of Canada, according to the report.
The review was preregistered under protocol INPLASY2025110004 and followed PRISMA reporting standards, according to the study. Two reviewers screened 5,240 deduplicated peer-reviewed records plus gray literature, with perfect inter-rater agreement (Kappa = 1.0), the authors reported. The study also used a quality assessment tool from the U.S. National Institutes of Health.
Funding disclosures included in the paper state that one author is a consultant with Merck, Sanofi, Moderna, Dynavax, and Seqirus, and that another author’s center receives funding from vaccine manufacturers, according to the report.
Transmission Rates and Case Characteristics
The review documented that among vaccinated measles cases, 70 of 890 (7.9%) transmitted to others, according to the study. The median number of secondary cases per transmitter was 2, with an interquartile range of 1 to 4, the authors reported. Of the transmitters with available dosing data, 22 of 70 (31.4%) had received two or more doses of the MMR vaccine, according to the paper.
The study also reported that only about one in three transmitters meeting the WHO clinical case definition of measles, suggesting milder symptoms may lead to undercounting, as the authors wrote. The authors stated in the paper that “this potential misclassification may mean that the true number of vaccinated cases included in our study is lower than 70,” according to the report. Research has shown that measles cases occur in populations with high vaccination rates, which is consistent with these findings, as prior reports from outbreak settings have documented cases among vaccinated individuals [3]. Additionally, the concept of waning immunity and breakthrough infections has been a documented concern in the scientific literature for years [1].
One Study Underpins Vaccine Effectiveness Estimates
The systematic review identified only one study, involving 137 people, that attempted to estimate adjusted vaccine effectiveness against onward transmission from already-infected vaccinated cases, according to the paper. That Dutch outbreak analysis reported 10% effectiveness for one dose (95% CI ?80 to +62) and 61% for two or more doses (95% CI ?203 to +100), according to the study’s authors.
The authors noted that the confidence intervals were wide due to the small sample size, particularly the 16-person two-dose group, as stated in the report. According to the review, the authors found no evidence to contradict current thinking that vaccinated cases are less likely to transmit, but the quantitative basis for this claim rests on this single small study, the paper’s findings suggest.
Limitations, Context, and Author Cautions
The study’s limitations section states that genotyping of measles virus was not always conducted, so chains of transmission cannot be certain, according to the report. The authors wrote that the 70 transmitters figure is likely an underestimate because not all outbreak investigations record vaccination history, as stated in the paper. They also noted that vaccinated cases often have milder symptoms and lower viral loads, which may explain lower transmission rates, the authors reported.
In the paper, the authors state that such transmissions “must be considered in public health investigations,” according to the report. They clarify that the findings do not indicate that the vaccine is ineffective, but rather document that transmission occurs, as the study states. This finding is significant because mainstream messaging has often framed measles outbreaks as being driven solely by unvaccinated individuals, a claim that this data complicates [2]. Furthermore, the review comes at a time when measles cases in the U.S. are at their highest level in 35 years, with 2,318 cases confirmed through July 23, 2026, according to CDC data [4]. The role of vaccinated individuals in transmission dynamics is a critical factor for public health investigations to consider, the study concludes.
References
- GreenMedInfo.com. “What is Going on With Measles: The Science and Politics of Eradicating Measles.”
- GreenMedInfo.com. “Measles Outbreak: Fake News and Mass Hysteria.”
- GreenMedInfo.com. “Measles Transmitted By The Vaccinated, Gov. Researchers Confirm.”
- ZeroHedge.com. “US Measles Cases In 2026 Highest In 35 Years.” July 30, 2026.
Explainer Infographic
Read full article here