In a sobering assessment this week, a leading US infectious disease expert declared that the world may have moved into a “post-herd immunity” era for measles, as vaccination gaps spark resurgent outbreaks across multiple countries. The statement comes as the United States faces its worst measles outbreak in decades, with more than 930 cases reported this year alone—a harbinger that the protective barrier of community immunity is crumbling (The Guardian, MSN).
This announcement carries urgent significance for Thai readers, as diminishing vaccine coverage worldwide increases the risk of measles returning to countries that had previously achieved disease control. On a global scale, measles had been “eliminated” from many regions—including the US and parts of Southeast Asia—thanks to decades of successful vaccination programmes. However, recent declines in vaccine uptake, fueled by misinformation, logistical disruptions, and pandemic-related hesitancy, threaten to unravel that legacy (Los Angeles Times).
The key fact driving this new risk is the concept of herd immunity: when about 95% of a population is immunized against a disease like measles, transmission chains are blocked, protecting even those who cannot be vaccinated, such as infants and people with certain medical conditions (CDC). Experts now warn that in many places this threshold is no longer being met. In recent interviews, the director of the Vaccine Education Center at a major US children’s hospital stated, “We’re living in a post-herd immunity world. I think the measles outbreak proves that,” underscoring that a single imported case can now ignite widespread transmission due to immunity gaps (The Guardian).
Public health data from the US and Europe reveal a troubling downtrend in childhood immunization rates post-pandemic. According to the World Health Organization (WHO), global measles vaccination rates fell to 83% in 2023—the lowest since 2008—jeopardizing decades of progress (WHO Measles Fact Sheet). In the US, federal health agencies have documented coverage below the 95% goal needed for herd immunity, with pockets of even lower rates, especially in communities influenced by anti-vaccine misinformation (NPR), mirroring trends observed in parts of Southeast Asia.
Measles is one of the most contagious viruses known: one infected person can spread the disease to up to 90% of nearby unvaccinated individuals. The symptoms—high fever, rash, cough, and conjunctivitis—can lead to severe complications such as pneumonia, brain swelling, blindness, and even death, particularly among young children (WHO). The resurgence of measles is not theoretical: 2024 and 2025 have seen spikes in reported cases in the United States, Great Britain, New Zealand, and several Asian and African countries, with clusters often forming in areas where vaccine refusal or scepticism has become widespread (WHO Weekly Epidemiological Update).
For Thailand, these developments are a critical wake-up call. Thai authorities had worked for decades to control measles, achieving high vaccination rates through school-based and child immunization campaigns (Thailand MoPH). However, recent surveys reveal signs of complacency, gaps in migrant populations’ vaccine access, and pandemic-driven service interruptions that risk creating susceptible clusters. A senior official from the Department of Disease Control—speaking on official record—warned, “Any lapse in routine immunization coverage can leave communities vulnerable. With international travel rebounding, a single imported case could trigger an outbreak if we let our guard down.”
Historically, Thailand has responded to outbreaks with rapid “ring vaccination” campaigns and public information drives. In 2019, officials swiftly contained a measles outbreak traced to Southern border provinces by mobilizing both public hospitals and local religious leaders to advocate for vaccination. A public health specialist from the National Vaccine Institute recalled, “Empowering village health volunteers and engaging community elders has always been key to regaining trust and boosting coverage.”
However, the new “post-herd immunity” reality means that isolated efforts may not suffice. If community protection drops below the critical threshold, those cannot be vaccinated—such as babies under one year and individuals with compromised immune systems—are at heightened risk. Pediatricians and infectious disease experts alike are calling for renewed investment in vaccination services, robust public information campaigns to counter social media misinformation, and catch-up drives for children whose routine immunizations were delayed during the pandemic (News Nation).
Globally, researchers estimate that a further drop in vaccination rates could result in more than 3 million additional hospitalizations and over 159,000 deaths annually from measles and its complications (News Nation). The burden would fall disproportionately on low- and middle-income countries, where vaccine access, cold-chain logistics, and health worker shortages already pose challenges—issues Thailand has historically tackled through donor partnerships and regionally coordinated campaigns. But experts now stress that even high-coverage nations are not immune in a globalized world.
Looking ahead, health officials urge swift and comprehensive action to restore full immunization coverage. The Centers for Disease Control and Prevention (CDC) recommend two doses of the measles-mumps-rubella (MMR) vaccine for all children, with “catch-up” policies for older unvaccinated children and adults at risk (CDC). Thailand’s Ministry of Public Health is reviewing strategies to address gaps among migrant communities, remote highland populations, and urban “pockets of resistance”—often communities influenced by online skepticism.
Culturally, vaccination has long been viewed as a civic and Buddhist duty in Thai society, protecting both the individual and their neighbors. Campaigns enlisting the support of monks, teachers, and village leaders have been shown to increase acceptance, as seen in the swift containment of rubella and polio. Reviving these collaborative traditions, alongside new digital outreach, could help overcome pandemic-era trust deficits and practical access barriers.
In summary, the world’s apparent move into a “post-herd immunity” era for measles must be met with vigilance and renewed collective responsibility. Thai parents are urged to ensure their children are fully immunized, especially before starting school or traveling abroad. Health workers recommend checking vaccine records for all household members and utilizing catch-up services where necessary. The public is advised to seek accurate, evidence-based information from sources such as the Ministry of Public Health, WHO, and reputable Thai hospitals, rather than unreliable social media posts.
The return of measles is not just a foreign problem. The lesson from recent outbreaks is stark: only by maintaining high immunization rates—together—can we prevent a disease long thought conquered from threatening a new generation.
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