Lesson 10 — What If...?
How Do Vaccines Actually Work?
Learning Material
1 pagesLesson 10 — What If...?
Understanding the Complex: How Do Vaccines Actually Work?
The best way to stress-test understanding is to push it to its limits — to ask not just what is, but what could be, and what would follow. Three thought experiments.
What if mRNA cancer vaccines work for all cancers?
The early melanoma data is encouraging. But melanoma is, in oncological terms, one of the more immunogenic tumors — the immune system is already partially active against it, which makes it a better candidate for immune-activating therapies. Cancers of the pancreas, liver, or brain are far more immunologically "cold," and there is no guarantee that mRNA-based neoantigen vaccines will work as well against them.
But suppose the Phase 3 melanoma trial succeeds, and the approach is validated broadly. What would follow?
The manufacturing challenge becomes central. A truly personalized mRNA cancer vaccine requires sequencing a patient's tumor, identifying neoantigens, designing the vaccine sequence, manufacturing it, and delivering it — ideally within weeks of diagnosis. At current costs and speeds, this would be expensive and logistically complex. Some estimates put the cost of manufacturing a personalized mRNA vaccine in the range of 100,000to200,000 per patient. If it works, the question becomes whether it can be made cheap enough to reach patients beyond wealthy health systems.
There are paths toward cost reduction: better algorithms for identifying neoantigens (reducing the sequencing and computation burden), shared antigen targets where mutations cluster across many patients (reducing the need for full personalization), and manufacturing automation. None of these paths are certain. The history of medicine is full of promising therapies that remained expensive for decades.
But if the approach works and costs come down — if a personalized cancer vaccine becomes a realistic option for patients with resectable solid tumors — it would represent a fundamental shift in oncology. Not a cure for all cancers, but a new category of tool that turns the immune system into a precision weapon against a specific tumor.
What if vaccine trust continues to erode?
Vaccine hesitancy has been growing in many high-income countries for reasons that are not going away: institutional distrust, social media misinformation ecosystems, politicization of health decisions, and the experience of COVID-era mandates that left residues of resentment. Measles — declared eliminated in the United States in 2000 — has returned in outbreaks driven by falling vaccination rates.
The public health consequences of continued erosion would be concrete. Diseases that are currently controlled by high vaccination coverage would become endemic again in communities with lower rates. Polio, which came within years of eradication before COVID disrupted vaccination campaigns, could spread. Novel pathogens that require rapid vaccine rollout would encounter a population with a meaningful fraction skeptical or refusing.
The harder question is what to do about it. The evidence suggests that aggressive pro-vaccine campaigns can sometimes backfire, increasing resistance among those already hesitant. The approaches that have worked better are local, trusted-messenger based, non-coercive, and patient. They treat hesitant people as people with legitimate concerns, not as defective patients to be corrected. Scaling such approaches is possible but requires investment and time.
There is no vaccine for distrust.
What if a new highly dangerous pathogen emerges tomorrow?
Suppose a novel pathogen — high transmissibility, high case fatality rate — is identified in a crowded city. Genomic sequencing is available within 24 hours. What happens?
Under current best-case assumptions: within days, mRNA vaccine candidates targeting the pathogen's surface proteins are designed. Within weeks, they are in Phase 1 trials. Within months, enough data exist to consider emergency use authorization. Manufacturing, which was the bottleneck in COVID, can now be pre-positioned if the platform is ready.
The counterfactual — what happens if the pathogen is genuinely novel and our existing platform infrastructure cannot quickly generate candidates — is more troubling. The mRNA platform is not universally applicable; it works best for pathogens with identifiable surface protein antigens. Some theoretical threat scenarios involve pathogens where antigen selection is not straightforward.
What is clear is that the world's preparedness for a novel pandemic has improved significantly since 2019 — partly because of infrastructure built during COVID, partly because the mRNA platform demonstrated a faster development timeline. What is also clear is that preparedness is not the same as immunity. A faster response reduces harm; it does not eliminate it.
The lesson of COVID — both the tragedy and the technological achievement — is that speed matters, that investment in basic science and platform technology pays off, and that the gap between what is scientifically possible and what is equitably delivered remains very large.
Next lesson: What are you taking away? — A course close on vaccines, the mRNA revolution, and what it connects to across the "Understanding the Complex" series.
Reading time: approx. 9–10 minutes