By GRANT K. STUDEBAKER, MD, FAAFP, FASAM

Measles, declared just 25 years ago to be eliminated in the United States, has returned in 2025 with unsettling force, producing the highest national case count in more than three decades. Tennessee has not escaped this resurgence, with six confirmed cases reported through July this year.

Although such numbers may appear modest at first glance, the epidemiological risk they represent is substantial. In communities where vaccination coverage has fallen below critical thresholds, even a few cases can trigger a large-scale outbreak. Measles is not merely contagious; it is among the most transmissible diseases known to humankind, with a basic reproduction number (R₀) estimated at 12 to 18, meaning a single infected individual can transmit the virus to an average of 12 to 18 susceptible contacts. By comparison, seasonal influenza has an R₀ of approximately 1 to 2, and COVID-19 has an R₀ of approximately 4.22 with a standard deviation of 1.69. This extraordinary transmissibility means that a very high proportion of the population must be immune to prevent sustained spread. Epidemiologic modeling shows that for measles, immunity must be maintained above roughly 92 to 94 percent to interrupt transmission. In practice, a target of at least 95 percent is necessary to account for the realities of population health, including imperfect vaccine response, rare cases of waning immunity, the continual entry of unvaccinated newborns, and clusters of under-immunized individuals. Falling below this threshold removes the protective buffer provided by herd immunity, allowing each imported case to ignite rapid chains of transmission that can transform a single exposure into a community-wide outbreak.

The measles, mumps and rubella (MMR) vaccine remains one of the safest and most effective tools in the modern medical arsenal. The two-dose series confer long-term immunity in approximately 97 percent of recipients. Yet, according to the CDC, the national kindergarten coverage for MMR has now fallen to around 92.5 percent, dipping below the herd immunity threshold. This decline reflects a confluence of factors: missed well-child visits and delayed immunizations during the COVID-19 pandemic, a rise in nonmedical exemptions in certain jurisdictions and persistent misinformation, particularly the thoroughly debunked claim linking MMR vaccine to autism. The erosion of public confidence in vaccines, fueled by social media echo chambers and political polarization, has transformed what should be a straightforward public health success into an urgent national challenge.

The national picture underscores the gravity of the situation. As of August 5, 2025, the United States has reported 1,356 confirmed measles cases across 41 jurisdictions, the highest total since 1992. Thirty-two documented outbreaks account for nearly 90 percent of cases. By mid-April alone, the nation had recorded 800 cases, representing a 180 percent increase over the total for 2024. Hospitalizations have occurred in 13 percent of patients, and three individuals have died. 92 percent of those infected were either unvaccinated or of unknown vaccination status, making this, not a failure of science, but of coverage.

Tennessee’s experience mirrors the broader national trend. As of April, 2025, six measles cases had been confirmed in the state, beginning with an index case in Rutherford County. Four cases were reported by early April, followed by two additional cases within weeks. All confirmed infections occurred in unvaccinated individuals. Although Tennessee has previously made substantial gains in childhood immunization, raising coverage for the combined seven-vaccine series among children aged 19 to 35 months from 44.8 percent in 2009 to 79.3 percent in 2017, progress has since stalled, and rates have begun to decline in some communities. The statewide nonmedical exemption rate remains relatively low at 1.9 percent, yet, this average masks dangerous geographic clustering. Even a small number of exemptions, when concentrated within schools or neighborhoods, can erode local herd immunity and create fertile ground for an outbreak.

Addressing this crisis requires a multi-pronged approach that integrates clinical practice, community engagement and policy reform. At the provider level, motivational interviewing (MI) has emerged as an effective, evidence-based strategy for addressing vaccine hesitancy. By employing empathetic, nonjudgmental dialogue and reflective listening, MI helps parents voice concerns and arrive at informed decisions grounded in trust rather than confrontation. Studies show that postpartum MI interventions significantly increase vaccine coverage at 3, 5, and 7 months of age. At the same time, providers should employ presumptive language, presenting vaccination as a routine and expected part of care, and pair it with a strong, confident recommendation. This approach has been consistently associated with higher uptake. Programs such as the CDC’s Immunization Quality Improvement for Providers (IQIP) initiative can further support clinicians in refining their communication skills and addressing barriers in their practice workflows.

Community engagement is equally essential to sustaining high immunization coverage. In populations with entrenched hesitancy, particularly where cultural or religious beliefs shape health decisions, partnerships with local and faith leaders can strengthen credible information and frame vaccination as a shared community responsibility. Culturally tailored messaging, delivered by trusted voices within the community, has been shown to increase acceptance and strengthen public confidence in vaccination.

From a policy perspective, Tennessee should focus on strengthening implementation of its existing statewide vaccination requirements rather than introducing new mandates. Under Tenn. Code Ann. § 49-6-5001, school immunization rules are uniform across the state, but enforcement could be enhanced by standardizing the process for claiming religious exemptions, requiring annual renewal on an affidavit, and auditing exemption patterns to identify and address geographic clustering. Consistent application of these measures, along with rapid exclusion protocols during outbreaks, would help close vulnerabilities in community protection. Policy should also address adult immunity. Adults born after 1957 should have documentation of at least one MMR dose, with two doses recommended for higher-risk groups such as healthcare personnel, college students, and international travelers. Those vaccinated with inactivated measles vaccine between 1963 and 1967, or with unknown vaccine type, should be revaccinated with a live MMR dose. While routine serologic testing is not necessary, it can be considered in select cases when documentation is uncertain.

Enhanced surveillance will be essential for early detection and rapid response. Tennessee’s electronic laboratory reporting and syndromic surveillance systems (tn.gov/health/cedep/reportable-diseases/measles-rubeola.html) already integrate clinical, laboratory and public health data, enabling the near real time identification of emerging clusters. Wastewater monitoring for measles, while not yet implemented in Tennessee, has shown promise in recent pilots elsewhere and could serve as an additional early warning tool in high-risk areas. Vaccination remains the primary defense, but established post-exposure prophylaxis with MMR vaccine within 72 hours of exposure and immune globulin within six days for susceptible high-risk individuals can help reduce the spread. There are currently no FDA approved antivirals for measles; however, investigational monoclonal antibodies and oral antivirals may eventually provide adjunctive options for severely ill or immunocompromised patients, particularly in healthcare settings.

The resurgence of measles is a preventable tragedy. Tennessee’s six cases in 2025 should not be dismissed as statistical noise; they are a warning beacon. Failure to act now risks allowing small sparks to ignite into statewide or regional outbreaks. Achieving and maintaining MMR coverage above 95 percent is both a scientific necessity and a moral imperative, one that will require coordinated commitment from clinicians, policymakers, community leaders and the public.

The tools to control measles are available, the evidence supporting their use is overwhelming, and the stakes could not be higher. As National Immunization Awareness Month provides a platform for renewed attention, Tennessee has an opportunity and an obligation to rebuild public trust, close coverage gaps and ensure that measles remains a preventable disease rather than a recurring reality. In public health, delay is the enemy; the time to act is now.

Sources

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