The Dangerous Return of Once-Controlled Infections
Throughout history, infectious diseases have ebbed and flowed, but modern public health advancements, especially vaccination, led many to believe that certain pathogens were permanently contained. However, recent years have proven this assumption wrong. A complex interplay of global travel, declining immunization, environmental changes, and other systemic factors has created a perfect storm for the re-emergence of diseases that were once considered vanquished. These resurgent infections, which include vaccine-preventable illnesses, drug-resistant bacteria, and zoonotic diseases, pose a significant and growing threat to global health security.
The Resurgence of Vaccine-Preventable Diseases
The alarming rise of measles
Measles, a highly contagious viral disease, provides one of the most prominent examples of a vaccine-preventable illness making a resurgence. Although declared eliminated in the U.S. in 2000, it has returned, primarily due to international travelers carrying the infection to unvaccinated communities. Data from 2025 shows a concerning spike in cases in the U.S., far surpassing totals from previous years, and outbreaks have occurred across multiple states. The key driver behind this spike is the erosion of herd immunity—the protection that occurs when a high percentage of the population is immunized, limiting the spread of a disease. This erosion is fueled by vaccine misinformation and a growing number of people opting out of vaccination.
Polio's persistent threat
Similarly, polio, a potentially fatal paralytic virus, remains a persistent threat globally. The poliovirus continues to circulate in different parts of the world, meaning that as long as it exists anywhere, it poses a risk everywhere. Anyone who is not fully vaccinated is vulnerable to serious illness. While vaccination has made polio extremely rare in most developed nations, the risk of a new outbreak in undervaccinated pockets of the population is real, underscoring the need for continued global vigilance.
Whooping cough on the rise
Pertussis, or whooping cough, is another vaccine-preventable disease that is increasing. In the first half of 2025, cases in the U.S. more than doubled compared to the same period in 2024, tragically leading to the deaths of several infants. The disease, known for its uncontrolled, violent coughing fits, is especially dangerous for young children, highlighting the importance of timely and consistent immunization for all age groups.
New Dangers from Old Diseases
Mpox: A re-emerging zoonotic threat
Mpox, formerly known as monkeypox, gained global attention during outbreaks in 2022 and 2023. While typically endemic to parts of Central and West Africa and spread from animals to humans, recent outbreaks have involved human-to-human transmission, particularly in dense urban areas. This shift is partly attributed to the decline of population immunity following the cessation of smallpox vaccinations, as the smallpox vaccine also offered protection against mpox. The circulation of more severe clades and unequal vaccine access continue to challenge public health efforts.
Cholera's grim return
One of the most ancient and treatable diseases, cholera, is experiencing a shocking comeback. The World Health Organization (WHO) reported a rise in global cases and a significant increase in deaths from cholera in 2024, particularly in vulnerable regions of Africa and the Middle East. This resurgence is directly linked to environmental and socioeconomic factors. Climate change-fueled extreme weather events, such as droughts and floods, can contaminate water sources, while conflict and income inequality can lead to breakdowns in sanitation infrastructure, creating a 'perfect storm' for the bacteria to thrive.
The fight against antibiotic resistance
Beyond viral and bacterial resurgences, a more insidious threat is the re-emergence of drug-resistant infections. The Centers for Disease Control and Prevention (CDC) has warned of a sharp increase in dangerous bacteria like NDM-CRE, which have developed resistance to multiple antibiotics. The overuse and misuse of antibiotics in both human medicine and agriculture are accelerating this problem, leading to the rise of so-called 'superbugs' that make infections harder and more expensive to treat. In this case, it's not a single disease that has come back, but rather entire categories of bacterial infections that are becoming untreatable with standard medicines.
Root Causes Behind the Comeback
Declining immunization rates
Misinformation and skepticism surrounding vaccines have directly contributed to a drop in immunization rates for a host of preventable childhood diseases, including measles, polio, and whooping cough. This trend is reversing decades of progress in disease control and leaving vulnerable populations, including infants and immunocompromised individuals, exposed to unnecessary risk.
Climate change and environmental shifts
As the planet warms, changes in climate are altering the behavior and habitat of disease vectors, such as mosquitoes and ticks. This has allowed diseases like Lyme disease and West Nile virus to expand into new geographic areas. Moreover, extreme weather events like floods and droughts can overwhelm sanitation systems and contaminate water supplies, fueling outbreaks of waterborne diseases like cholera.
Socioeconomic and systemic factors
Global travel, urbanization, poverty, and weak public health infrastructure all play a role in disease re-emergence. Overcrowded living conditions in cities can accelerate disease transmission, while international travel can quickly carry pathogens across the globe. Health inequities mean that marginalized communities are often disproportionately affected, facing barriers to healthcare and living in conditions conducive to disease spread. The diversion of resources during crises like the COVID-19 pandemic also created gaps in surveillance and immunization programs, further enabling the resurgence of other diseases.
Comparison of Resurgent Diseases
| Feature | Measles | Cholera | Mpox | Antibiotic Resistance |
|---|---|---|---|---|
| Transmission | Highly contagious airborne droplets, direct contact | Contaminated food and water | Close contact with infected persons/animals | Direct person-to-person contact, environmental spread |
| Key Drivers | Declining vaccination rates, international travel | Climate change, poor sanitation, conflict | Zoonotic spillover, human adaptation, waning immunity | Antibiotic overuse, poor infection control |
| Primary Prevention | Vaccination (MMR vaccine) | Safe water, sanitation, oral rehydration, vaccines | Vaccination for at-risk individuals, hygiene | Appropriate antibiotic use, infection control protocols |
| Affected Populations | Unvaccinated individuals (especially infants) | Vulnerable communities with limited clean water | At-risk communities and travelers | Anyone with bacterial infections, especially in healthcare settings |
Prevention and Moving Forward
The resurgence of these diseases is a clear call for renewed focus on public health. The path forward requires a multi-pronged approach:
- Reinforce Vaccination Programs: Addressing vaccine hesitancy through education and ensuring high immunization coverage is paramount, especially for highly contagious diseases like measles.
- Strengthen Public Health Infrastructure: Investing in robust surveillance, sanitation, and healthcare systems is vital, particularly in vulnerable communities and low-resource settings.
- Combat Climate Change and Inequities: Addressing the root causes that exacerbate disease spread, such as climate change and systemic inequality, is a long-term but necessary strategy.
- Promote Antibiotic Stewardship: Responsible use of antibiotics by both healthcare providers and patients is crucial to slowing the development of drug-resistant bacteria.
Conclusion
While a single answer to the question "what disease has come back?" is impossible, the underlying reasons for their return are surprisingly consistent. The global interconnectedness that enables rapid travel and the systemic vulnerabilities in our public health systems create opportunities for pathogens to thrive once more. Preventing future resurgences will require a concerted, global effort to address the root causes, from vaccine misinformation to climate change, and re-invest in the foundational public health measures that once kept these dangers at bay.
World Health Organization information on infectious disease resurgence
