Measles Vaccine Coverage Persists Well Below Herd Immunity Threshold

In the 20 months following postelimination outbreaks of the measles, measles-mumps-rubella (MMR) vaccination coverage remained below the proper thresholds for herd immunity, defined as 93% of a community’s population being vaccinated, according to a study published in JAMA Network Open.¹

“Measles is a highly contagious, vaccine-preventable disease that requires high population-level immunity to prevent sustained transmission,” wrote the authors of the study. “Among children older than 12 months, the MMR vaccine is estimated to be 93% effective after 1 dose and 97% effective after 2 doses. In the World Health Organization (WHO) Region of the Americas, measles vaccination coverage must exceed 93% to maintain herd immunity.”

Despite a seemingly collective effort to achieve herd immunity against measles in countries all around the world, developed nations like the US have experienced postelimination measles outbreaks at unprecedented rates. According to the CDC, these postelimination outbreaks—which are the resurgence of diseases not typically seen in medical practice or those known to be eradicated²—have resulted in a total of 1514 confirmed measles cases reported in 42 states this year alone.³

To achieve herd immunity against a vaccine-preventable disease, WHO definitions claim 93% of patients within a specific locale must be vaccinated. | image credit: digicomphoto / stock.adobe.com

READ MORE: California and West Coast States Release Recommendations on Respiratory Vaccination

While medical experts in the US reported a full eradication of the disease in 2000, sporadic outbreaks throughout this century have led to the potential of a reversal of that eradication. By the middle of 2025, the largest measles outbreak in Texas resulted in over 750 cases.⁴

Amid these concerning rises in measles cases not just in the US but globally, many providers are looking toward the efficacy of vaccination, making concerted efforts to relay to the general public the importance of receiving MMR vaccination and keeping communities protected.

“In response to the outbreak, public health officials implemented a range of interventions, including outbreak notifications, quarantines, daycare closures, and walk-in vaccination clinics,” they continued.¹ “However, widespread vaccine hesitancy limited MMR vaccine uptake. This study uses electronic medical records (EMRs) to assess MMR vaccination coverage over time, including timely receipt of MMR1 and MMR2, and identifies persistent postoutbreak immunity gaps.”

With the primary objective being trends in MMR coverage following an outbreak in Ohio, researchers conducted a cross-sectional study consisting of data from a central Ohio pediatric care network that served approximately 150,000 children. Children participating in the study and their coverage trends were observed at 3 specific time points: the onset of the measles outbreak (October 8, 2022), 12 months after the outbreak, and 20 months after.

Children were only included in the analysis if they were under 15 years old and had at least one pediatric visit in the previous 2 years. Further defining their key study end points, primary outcomes included "(1) timely MMR vaccine 1 receipt by 16 months of age, (2) timely MMR vaccine 2 receipt 28 days or more after MMR vaccine 1 and by 84 months of age, and (3) receipt of 1 valid MMR dose or more by 84 months of age. Coverage was assessed at each time point."¹

With participants conducting visits throughout the 20-month study period, the cohorts included in this study increased as time went on. Indeed, the analysis included a total of 133,476 participants at the onset of the measles outbreak, increasing to 143,720 at 12 months, and concluded with 149,092 at 20 months (median age, 7.96 years; 51.3% male).

After data collection, researchers uncovered that the first dose of MMR went unchanged throughout the period, starting at 53.6% of coverage for the cohort and ending at the same level 20 months after the onset of the outbreak. The second MMR doses increased slightly from 57.9% at onset to 60.2% after 20 months. Finally, coverage of at least 1 dose by 84 months of age increased from 77.3% to 77.9% throughout the study.

“This repeated cross-sectional study found that MMR vaccination coverage remained well below the herd immunity threshold across all key metrics up to 20 months after a large postelimination measles outbreak in central Ohio,” they wrote.¹ “Despite targeted containment efforts during the outbreak, timely MMR1 coverage remained unchanged, and only modest gains were observed in timely MMR2 and overall vaccine receipt.”

Regardless of the coverage increase observed in this analysis, significant gaps in measles immunity remain, as the highest rates of MMR coverage within this study (77.9%) were still considerably below the 93% herd immunity threshold. As outbreaks and community-wide vaccine hesitancy persist, experts and providers will need to improve efforts to reach the ideal herd immunity levels.

“In this repeated cross-sectional study of an extensive pediatric primary care network in central Ohio, MMR vaccination coverage remained well below the herd immunity threshold across all primary metrics 20 months after a major postelimination measles outbreak,” concluded the authors.¹ “These findings suggest the urgent need for targeted, data-informed public health strategies and ongoing surveillance to close immunity gaps and sustain measles elimination in the US.”

READ MORE: Immunization Resource Center

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REFERENCES

1. Martoma RA, Martoma JC, Majumder MS. Measles vaccination coverage after a postelimination outbreak. JAMA Netw Open. 2025;8(9):e2533732. doi:10.1001/jamanetworkopen.2025.33732

2. Knobler S, Lederberg J, Pray LA. The challenges to post-eradication outbreaks. National Academies Press (US). 2002. Accessed September 29, 2025. https://www.ncbi.nlm.nih.gov/books/NBK98115/

3. Measles cases and outbreaks. CDC. April 25, 2025. Accessed September 29, 2025. https://www.cdc.gov/measles/data-research/index.html

4. Godoy M. U.S. measles cases hit highest level in 33 years, CDC reports. NPR. July 9, 2025. Accessed September 29, 2025. https://www.npr.org/sections/shots-health-news/2025/07/09/nx-s1-5461155/measles-outbreak-cdc-vaccination-health