Exploring the scientific breakthroughs, ethical dilemmas, and practical challenges in humanity's quest to eliminate deadly pathogens.
Eradicated so far
Primary tool for eradication
Unintended consequences
Revolutionizing the fight
Few achievements in medicine rival the complete eradication of a disease. In 1980, the World Health Organization made a historic declaration: smallpox, a scourge that had killed hundreds of millions, was gone from the human population. For the first time, a microbial foe had been deliberately pushed to extinction. This monumental victory sparked both hope and a difficult question: could we, and should we, do this again?
Smallpox is one of only two infectious diseases that have been successfully eradicated. The other is rinderpest, which affected cattle.
Since smallpox, no human disease has been eradicated despite significant efforts against polio, guinea worm, and malaria.
Since that triumph, only one other human disease—rinderpest, which affected cattle—has been eradicated. The path forward is far more complex than early optimists imagined. It involves not just scientific breakthroughs but also navigating ecological nuances, ethical dilemmas, and the very real-world challenges of human behavior and healthcare access. As we stand at the frontier of new technologies, this article explores the captivating science, the sobering realities, and the moral calculations behind one of humanity's most ambitious goals.
Eradication is defined as the "permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts" 8 . This is different from elimination, which is control at a regional level, or extinction, where the pathogen no longer exists anywhere, including labs 8 . Successful eradication is a deliberate human endeavor that requires a very specific set of biological and practical conditions to be met.
The story of smallpox, the eradication poster child, reveals this perfect storm. The smallpox virus had no animal reservoir, meaning it could only spread from person to person. It had no latent or hidden phase; infected individuals showed obvious symptoms, making them easy to identify and isolate. Furthermore, an effective, single-dose vaccine that provided long-lasting immunity was available 1 . Denied access to new hosts through vaccination, the virus had nowhere to go and simply died out.
Other pathogens present even greater challenges. Herpes simplex virus hides latent in our neurons for life, reactivating periodically. Influenza A virus constantly changes its surface proteins through "antigenic drift and shift," forever staying one step ahead of our immune systems 1 . Many bacteria, like E. coli, live harmlessly in animal reservoirs or the environment, waiting for an opportunity to cause disease. For these microbes, eradication with our current technology is a biological near-impossibility 1 .
While eliminating a deadly disease seems an unalloyed good, science is revealing that our relationship with microbes is more complex than a simple war. Sometimes, the act of eradication can have unexpected, and sometimes negative, consequences, forcing us to ask not just "can we," but "should we?"
This bacterium is a known culprit, responsible for the vast majority of stomach ulcers and gastric cancers. Its widespread decline, thanks to improved hygiene and antibiotics, has led to a welcome drop in these diseases 1 .
However, researchers have discovered a puzzling correlation: as H. pylori colonization has fallen, there has been a reciprocal rise in the incidence of gastro-esophageal reflux disease and a related cancer, esophageal adenocarcinoma 1 . It appears that this longtime resident of the human stomach may, for some people, play a protective role.
This bacterium is a leading cause of pneumonia. Vaccines against it are lifesavers for vulnerable individuals. However, this bacterium is also a common member of our nasal flora, and studies suggest that when we vaccinate against it, we may be unintentionally disrupting the microbial ecosystem.
Colonization by vaccine-targeted strains of S. pneumoniae appears to be negatively associated with colonization by S. aureus, a more dangerous pathogen. Removing the first may open a niche for the second, potentially driving the rise of community-acquired methicillin-resistant S. aureus (MRSA) infections 1 .
We are learning that "bugs don't equal disease" 1 . The human body is an ecosystem, and the elimination of one microbe can create a vacuum that is filled by another, with consequences we cannot always predict.
These cases do not argue against fighting disease, but they do highlight a new, more nuanced understanding. As we contemplate eradicating other infections, we must invest in research to fully understand these intricate relationships we have co-evolved with our microscopic companions.
The battle against infectious diseases is being revolutionized by a new arsenal of technologies that enhance our abilities in prevention, detection, and response. These tools are making the goal of eradication more feasible, even for stubborn pathogens.
| Tool | Category | Function | Example |
|---|---|---|---|
| mRNA Vaccine | Prevention | Teaches cells to make a protein that triggers an immune response; rapidly adaptable. | COVID-19 vaccines 3 |
| Wastewater Surveillance | Surveillance | Monitors community-level pathogen spread by testing sewage; allows for early outbreak detection. | Tracking SARS-CoV-2 and its variants 3 |
| Next-Generation Sequencing (NGS) | Diagnosis | Sequences all genetic material in a sample to identify any pathogen without prior assumption. | Diagnosing rare or atypical infections 3 |
| Bacteriophages | Treatment | Viruses that specifically target and destroy bacterial cells; used against drug-resistant infections. | Treating multidrug-resistant Pseudomonas infections 3 |
| Long-Active Antiretrovirals | Treatment | Injectable formulations that provide sustained drug release, reducing dosing frequency from daily to monthly or bimonthly. | HIV treatment regimens 3 |
While laboratory experiments are crucial, some of the most important "experiments" in global health are conducted through mathematical modeling. These simulations allow scientists to project the future impact of different strategies, helping policymakers decide where to invest resources. A landmark 2021 study published in PLoS Medicine did exactly this, modeling the potential impact of the UNAIDS 2025 targets on ending AIDS as a public health threat by 2030 6 .
The researchers used a sophisticated mathematical simulation model called the Goals model to project the trajectory of the HIV epidemic 6 . The procedure was as follows:
The model was calibrated using decades of real-world historical data from 77 high-burden countries.
Researchers created "business-as-usual" and "ambitious targets" scenarios projecting to 2030.
The model factored in societal enablers and COVID-19 disruptions.
Results were cross-checked against two other independent models.
The results of this modeling experiment were striking. The data showed that achieving the 2025 targets would have a transformative effect on the global HIV epidemic.
The study also quantified the cost of inaction. It found that a lack of progress on critical societal enablers like fighting stigma and discrimination could result in an additional 2.6 million cumulative HIV infections and 440,000 AIDS-related deaths between 2020 and 2030 6 .
Achieving these targets would bring the world close to the ultimate goal of reducing new HIV infections and AIDS-related deaths by 90% between 2010 and 2030 6 . The analysis suggested that by 2025, the number of people living with HIV would actually start to decline—a clear signal that the epidemic was being reversed.
This modeling experiment provides more than just optimistic numbers; it offers a validated roadmap. It demonstrates that with a precise, targeted, and holistic strategy—one that combines medical intervention with social support—the eradication of AIDS as a public health threat is an achievable goal.
The question of whether we can and should eradicate infectious diseases has no simple answer. The triumphant eradication of smallpox shows us that it is possible, while the long, complex fights against polio, HIV, and others reveal the immense biological and societal hurdles. We are learning that our relationship with microbes is a delicate balance, where victory in one battle may unpredictably shift the ecosystem.
The Chinese CDC defines resilience as "the capacity to effectively prevent, detect, respond to, and control outbreaks without seriously affecting essential functions of health and social systems" .
Yet, the pursuit remains one of humanity's most noble endeavors. The journey itself—the scientific innovation, the strengthened health systems, the global cooperation—yields profound benefits. It builds the resilience we need to face the next health threat, known or unknown.
Eradication may be the ultimate finish line for a select few diseases, but the relentless pursuit of it forges a healthier, safer world for all.