Why measles outbreak in Pennsylvania poses risks beyond US borders

The United States is facing its largest outbreak of measles since the virus was declared eliminated in 2000.

Horses pull a wagon past a Lancaster County farm in Christiana, Pennsylvania, the US on October 20, 2026 [Matt Rourke/AP]

Decades after it was officially declared eliminated in the United States, measles has made a resurgence, with the US Centers for Disease Control and Prevention (CDC) announcing the third death of the year from the virus.

Matt Ferrari, director of Pennsylvania State University’s Center for Infectious Disease Dynamics, said the US was so successful at wiping out measles that it had “the luxury to forget” it was a serious problem.

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“It’s been a long time, and for many of us in the United States, and in fact, throughout the Western Hemisphere, we have been able to forget how nasty measles is,” Ferrari told Al Jazeera.

Pennsylvania has been hit especially hard in the most recent outbreak. In September, the state sought emergency support from the CDC to control the spread, even as state and federal health officials quarrelled over the measles-associated death tally — differing over how deaths should be classified. State officials have recorded more than 1,200 cases and over 240 hospitalisations in 42 counties so far this year.

This spike in cases has raised concerns in neighbouring US states. On October 5, New York Governor Kathy Hochul declared a state disaster emergency in response to rising cases in rural areas, expanding the number of health professionals authorised to vaccinate and test people for measles.

“No one should get seriously ill or die from a vaccine-preventable disease,” Hochul said.

But experts warn that the risks extend far beyond US state borders. The US resurgence comes as measles cases increase globally , particularly in communities that are vaccine-sceptical or where there are gaps in healthcare access.

Vaccination coverage among US kindergartners has decreased from 95.2 percent during the 2019-2020 school year to 92.4 percent in the 2025-2026 school year. Experts warn that declining vaccination rates in one geographic location can leave people thousands of miles away vulnerable, making measles prevention a shared global responsibility.

Building trust in vaccine-sceptical communities

Pennsylvania reported in August that two unvaccinated people died of measles in Lancaster County, which is located in the South Central part of the state. Lancaster is considered the centre of Pennsylvania Dutch Country and home to the nation’s oldest Amish and Mennonite communities, both of which have under-vaccinated populations.

In Pennsylvania, public health officials have worked with community leaders to share information and expand access to vaccination. Joshua Good, principal of Ephrata Mennonite School in Lancaster County, where two students contracted measles earlier this year, worked with state officials to organise a pop-up vaccination clinic at the school.

He said officials also provided communication materials that the school adapted for its community and helped identify at-risk families.

A flyer is displayed at a Pennsylvania Department of Health measles vaccination clinic located in Lancaster County in Peach Bottom, Pennsylvania, the US, October 20, 2026 [Matt Rourke/AP]

While Good said the response was productive, he told state officials that the Mennonite community still holds a lot of vaccine scepticism.

“I said, look, if we do this, keep in mind, our community by and large…made that decision not because they don’t have access to the vaccines. They made the decision based on their own best judgement,” he told Al Jazeera.

Good, who is vaccinated and vaccinated his children, sees himself as an advocate within the community. If families have questions about measles shots, he will answer them as best he can.

“I have honest conversations with people, try to engage in respectful, charitable ways,” he said. “I’ll try to understand what their hesitancies are. That said, I respect their concerns.”

Although multiple community members received the measles vaccine at the Ephrata clinic, vaccination rates remain below the threshold for herd immunity.

An Amish buggy travels through farm country on March 8, 2026, in Lancaster County, Pennsylvania, the US [Robert F Bukaty/AP]

Public health officials advocate for investing in robust community outreach before outbreaks happen.

“You can’t just show up in a community in an emergency– an emergency in which they might feel like you’re there to kind of blame them or shame them,” Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health, told Al Jazeera. “You need to know them so that they see public health as a resource rather than law enforcement.”

She said low vaccination coverage and distrust of the government allow measles to spread even when vaccines are available. But that shouldn’t stop governments from building rapport with vaccine-sceptical communities.

“I worry that by framing it around their demographics, it lets governments off the hook in terms of what they’re supposed to be doing, which is stopping the spread of this dangerous disease,” Nuzzo said.

Experts explain that declining vaccination rates put not only these communities but also immunocompromised people at greater risk for disease. Herd immunity in the wider population formerly helped shield those most vulnerable to infection.

“Those are communities that have been at risk for years,” Ferrari said. “But higher rates of vaccination in the communities surrounding them offered a barrier.”

Vendors sell produce at the Lancaster Central Market, March 7, 2026, in Lancaster County, Pennsylvania, the US [Robert F Bukaty/AP]

A shared global risk

The continental Americas was the first World Health Organization (WHO) region to eliminate endemic measles transmission in 2016. Maintaining that status requires high and consistent vaccination coverage. The Pan American Health Organization (PAHO) says coverage across the region remains below the target for both doses of the measles vaccine, contributing to noticeable consequences.

PAHO holds an annual RVC Measles Elimination Status Conference where an independent technical body of international experts monitors and reviews whether countries in the Americas have successfully eliminated measles, rubella, and congenital rubella syndrome. A country can lose its “elimination status” when the same measles virus genotype has circulated continuously for at least 12 months.

Last year, Canada became the first country in the continental Americas to lose its status after an outbreak that began in 2024. Some have warned that the US may be on track to lose its status this year.

But Dr Daniel Salas, executive manager of the Special Program for Comprehensive Immunisation at PAHO, told Al Jazeera that it’s not just the US that will be under review.

“We have Mexico, we have Bolivia that is going to be closely assessed because they could potentially lose status as well,” he said.

US Health and Human Services Secretary Robert F Kennedy Jr has repeatedly defended the US response to measles.

“We’re doing a better job than any country in the world at controlling the measles outbreak,” Kennedy said at an August 26 event in Florida. He cited higher case numbers in Mexico, Canada and Britain.

But Nuzzo said the repeated outbreaks across the US point to a country struggling to contain transmission.

“We have not seen it this bad,” she said. “It’s like this perpetual game of Whac-A-Mole. As long as there are vulnerable communities, as long as we don’t have strategies for early detection and rapid response and containment, measles will just keep on happening over and over and over again.”

Dr Salas told Al Jazeera that action within the first three days after a suspected case is critical, and health authorities should begin investigating and taking response measures without waiting for laboratory confirmation. Delays of a week or more can allow the highly contagious virus, marked by fever, coughing, and a whole-body rash, to spread further.

Experts warn that outbreaks cannot be treated as isolated local events. Scientific journals have found evidence that the virus strain in Canada’s latest measles outbreak was genetically linked to cases reported in US Mennonite communities. This was the same outbreak that resulted in Canada losing its measles elimination status.

“The spread of measles in the United States imperils other countries,” said Nuzzo. “It’s easy to kind of point to other countries and say that they’re the problem, but the reality is we’re all dependent on each other, and it’s very hard to protect ourselves when measles is spreading elsewhere.”

美国正面临自 2000 年宣布麻疹病毒被消除以来最大规模的麻疹疫情。

2026年10月20日，在美国宾夕法尼亚州克里斯蒂安娜，马匹拉着一辆马车经过兰开斯特县的一个农场。[Matt Rourke/AP]

麻疹在美国被正式宣布消除数十年后，又卷土重来。美国疾病控制与预防中心 (CDC) 宣布，今年已有第三人死于该病毒。

宾夕法尼亚州立大学传染病动力学中心主任马特·法拉利表示，美国在消灭麻疹方面取得了巨大成功，以至于它“有余力忘记”麻疹是一个严重的问题。

（共3位共和党参议员之一）在麻疹死亡人数上升之际抨击特朗普疫苗政策

孟加拉国麻疹死亡人数超过1000人，疫苗接种活动效果不佳（共3个列表，此为第2个）

列表 3（共 3 条）：尽管疫苗接种运动创纪录，孟加拉国仍因麻疹失去 1000 人，原因何在？

“已经过去很久了，对于我们美国的许多人来说，事实上，对于整个西半球的许多人来说，我们已经忘记了麻疹有多么可怕，”法拉利告诉半岛电视台。

在最近一次疫情爆发中，宾夕法尼亚州受到的冲击尤为严重。9月份，该州向美国疾病控制与预防中心（CDC）寻求紧急援助以控制疫情蔓延，与此同时，州和联邦卫生官员在麻疹相关死亡人数的统计上存在分歧——双方在死亡病例的分类方式上存在分歧。今年迄今为止，该州42个县已记录了超过1200例病例和240多例住院病例。

病例激增引发了邻近美国各州的担忧。10月5日，纽约州州长凯西·霍楚宣布该州进入灾难紧急状态，以应对农村地区病例的增加，并扩大了获准为民众接种麻疹疫苗和进行麻疹检测的医护人员数量。

“任何人都不应该因疫苗可预防的疾病而患上重病或死亡，”霍楚说。

但专家警告说，风险远不止于美国各州边界。美国麻疹疫情的再次爆发正值全球麻疹病例增加之际，尤其是在那些对疫苗持怀疑态度或医疗服务匮乏的社区。

美国幼儿园儿童的疫苗接种率已从2019-2020学年的95.2%下降到2025-2026学年的92.4%。专家警告说，一个地区的疫苗接种率下降可能会使远在千里之外的人们面临感染风险，因此预防麻疹是全球共同的责任。

在对疫苗持怀疑态度的群体中建立信任

宾夕法尼亚州8月份报告称，兰开斯特县有两名未接种疫苗的人死于麻疹。兰开斯特县位于该州中南部，被认为是宾夕法尼亚荷兰乡村的中心，也是美国历史最悠久的阿米什人和门诺派教徒社区的所在地，这两个社区的疫苗接种率都较低。

在宾夕法尼亚州，公共卫生官员与社区领袖合作，分享信息并扩大疫苗接种渠道。兰开斯特县埃弗拉塔门诺派学校的校长约书亚·古德与州政府官员合作，在该校组织了一次临时疫苗接种活动。今年早些时候，该校两名学生感染了麻疹。

他说，官员们还提供了学校根据社区情况进行调整的宣传材料，并帮助识别高危家庭。

2026年10月20日，美国宾夕法尼亚州桃底镇兰开斯特县的宾夕法尼亚州卫生部麻疹疫苗接种诊所展示着一份宣传单。[Matt Rourke/AP]

古德表示，虽然应对措施富有成效，但他告诉州政府官员，门诺派社区仍然对疫苗抱有很大的怀疑态度。

“我说，听着，如果我们这样做，请记住，我们社区的大多数人……做出这个决定并不是因为他们无法获得疫苗。他们是根据自己最好的判断做出的决定，”他告诉半岛电视台。

古德本人及其子女都接种了疫苗，他认为自己是社区里的疫苗倡导者。如果家属对麻疹疫苗有任何疑问，他会尽力解答。

他说：“我会与人坦诚交流，尽量以尊重和友善的方式与他们沟通。我会努力理解他们的顾虑。也就是说，我尊重他们的担忧。”

尽管许多社区成员在埃弗拉塔诊所接种了麻疹疫苗，但疫苗接种率仍低于群体免疫的阈值。

2026年3月8日，一辆阿米什马车行驶在美国宾夕法尼亚州兰开斯特县的农田中。[Robert F Bukaty/AP]

公共卫生官员主张在疫情爆发前加大对社区宣传的投入。

“你不能在紧急情况下贸然出现在社区——在这种紧急情况下，他们可能会觉得你是来指责或羞辱他们的，”布朗大学公共卫生学院疫情中心主任詹妮弗·努佐告诉半岛电视台。“你需要了解他们，让他们把公共卫生视为一种资源，而不是执法部门。”

她表示，疫苗接种率低和民众对政府的不信任导致麻疹即便在疫苗充足的情况下仍然传播。但这不应阻止政府与对疫苗持怀疑态度的群体建立良好关系。

努佐说：“我担心，如果以人口统计数据为框架来讨论这个问题，就会让政府逃避他们应该做的事情的责任，那就是阻止这种危险疾病的传播。”

专家解释说，疫苗接种率下降不仅使这些社区，也使免疫功能低下的人群面临更大的疾病风险。过去，群体免疫在更广泛的人群中发挥了保护作用，使最易感染人群免受感染。

“这些社区多年来一直面临风险，”法拉利说。“但周边社区较高的疫苗接种率起到了一定的阻隔作用。”

2026年3月7日，美国宾夕法尼亚州兰开斯特县兰开斯特中央市场，商贩们正在售卖农产品。[Robert F Bukaty/AP]

全球共同风险

2016年，美洲大陆成为世界卫生组织（世卫组织）首个消除麻疹地方性传播的区域。维持这一状态需要高且持续的疫苗接种覆盖率。泛美卫生组织（PAHO）指出，该区域麻疹疫苗两剂接种率仍低于目标值，并造成了显著的后果。

泛美卫生组织每年举办一次RVC麻疹消除状况会议，由一个独立的国际专家技术机构负责监测和审查美洲各国是否已成功消除麻疹、风疹和先天性风疹综合征。如果同一种麻疹病毒基因型连续流行至少12个月，则该国可能失去“消除状态”。

去年，加拿大成为美洲大陆第一个因疫情爆发（疫情始于2024年）而失去豁免权的国家。一些人警告说，美国今年可能也会失去豁免权。

但泛美卫生组织全面免疫特别规划执行经理丹尼尔·萨拉斯博士告诉半岛电视台，受到审查的不仅仅是美国。

他说：“墨西哥和玻利维亚的情况将受到密切评估，因为它们也可能失去地位。”

美国卫生与公众服务部部长小罗伯特·F·肯尼迪曾多次为美国应对麻疹疫情的措施辩护。

肯尼迪在8月26日于佛罗里达州举行的一次活动上表示：“我们在控制麻疹疫情方面比世界上任何一个国家都做得更好。”他列举了墨西哥、加拿大和英国更高的病例数。

但努佐表示，美国各地反复爆发疫情表明，该国难以控制疫情传播。

“我们从未见过这么糟糕的情况，”她说。“这就像一场永无止境的打地鼠游戏。只要存在易感人群，只要我们没有早期发现、快速反应和控制的策略，麻疹就会不断反复爆发。”

萨拉斯博士告诉半岛电视台，疑似病例出现后的前三天内采取行动至关重要，卫生部门应立即展开调查并采取应对措施，无需等待实验室确诊结果。如果拖延一周或更长时间，这种传染性极强的病毒（其症状包括发烧、咳嗽和全身皮疹）可能会进一步传播。

专家警告说，疫情爆发不能被视为孤立的局部事件。科学期刊已发现证据表明，加拿大最近一次麻疹疫情中的病毒株与美国门诺派社区报告的病例存在基因关联。正是这次疫情导致加拿大失去了消除麻疹的地位。

努佐说：“麻疹在美国的蔓延危及其他国家。人们很容易把矛头指向其他国家，说他们才是问题所在，但现实是我们彼此依赖，当麻疹在其他地方蔓延时，我们很难保护自己。”