teach the immune system to recognize and destroy tumours
mRNA vaccines demonstrated 87% effectiveness against COVID infection and 94% against mortality in real-world data spanning 2020-2025. Rare heart inflammation side-effects from vaccines are milder and less frequent than heart complications from actual COVID infection.
- 87% effectiveness against COVID infection; 94% against mortality (2020-2025 data)
- Rare heart inflammation from vaccines is milder and less frequent than from actual COVID
- Personalized mRNA cancer vaccines are in clinical trials, custom-built for each patient's tumor mutations
A Lancet review confirms mRNA vaccines are safe and effective against COVID-19, with 87% effectiveness against infection and 94% against mortality. The technology now shows promise for personalized cancer treatments.
A sweeping review of six years of mRNA vaccine data, published this week in The Lancet, confirms what billions of doses have already suggested: the technology is safe, it works against COVID-19, and it may be about to transform how we treat cancer.
Dr. Manish Sadarangani and his team at B.C. Children's Hospital spent months sifting through laboratory studies, clinical trials, and real-world surveillance records from Pfizer-BioNTech and Moderna vaccines administered between January 2020 and December 2025. What they found was reassuring on the fundamentals. The vaccines showed 87 percent effectiveness against documented COVID infection and 94 percent effectiveness against death in the two to six weeks following vaccination. Those numbers matter because they represent not theoretical promise but actual outcomes across billions of arms worldwide.
The mechanism itself remains elegant in its simplicity. Unlike traditional vaccines that introduce a weakened piece of the virus, mRNA vaccines deliver genetic instructions that tell your cells to manufacture the spike protein themselves. Your immune system then learns to recognize and destroy that protein, building defenses before it ever encounters the real virus. The approach was decades in the making but was compressed into months during the pandemic.
One finding the researchers emphasized was context. Yes, rare cases of myocarditis and pericarditis—inflammation of the heart muscle and its surrounding membrane—have been documented after vaccination. But getting COVID itself carries a far higher risk of the same complications, and the vaccine-related cases tend to be milder. Matthew Miller, a virologist at McMaster University who reviewed the study, called this distinction crucial. "It's a signal we should watch out for," he said, "but it's also important to contextualize the relative infrequency of that adverse event in relation to the clear, overarching benefit of vaccination." Miller suggested that much of the vaccine hesitancy that persisted in some communities wasn't rooted in concerns about the shots themselves but rather in broader anxieties about medical authority and choice.
But the review's gaze extends beyond COVID. The same immune-teaching logic that works against viruses can be retrained to recognize and destroy cancer cells. Dr. Ramy Saleh at McGill University is part of a global clinical trial testing this approach in bladder cancer patients. The process is painstaking and personalized. Surgeons remove the tumor, scientists sequence its DNA to identify mutations unique to that specific cancer, and then a custom mRNA vaccine is designed and administered to prime the patient's immune system to hunt down any remaining malignant cells. "If our immune system knows that there are cancer cells and attacks them, the chances of a relapse or the cancer coming back will be much lower and the chances of a cure increase," Saleh explained. This is medicine tailored to the individual, not mass-produced for the population.
What makes this moment significant is the bridge between what we know works and what we're about to learn. The pandemic forced mRNA technology out of the laboratory and into the real world at unprecedented scale. Billions of doses provided a natural experiment in safety. Now, with that foundation solid, researchers are asking what else this platform can do. The next chapter won't be written in emergency rooms or vaccination clinics. It will unfold in oncology wards, one patient at a time.
Notable Quotes
If our immune system knows that there are cancer cells and attacks them, the chances of a relapse or the cancer coming back will be much lower and the chances of a cure increase.— Dr. Ramy Saleh, McGill University oncologist
It's important to contextualize the relative infrequency of that adverse event in relation to the clear, overarching benefit of vaccination.— Matthew Miller, McMaster University virologist
The Hearth Conversation Another angle on the story
Why does a review of old data matter now? Aren't we past the COVID moment?
Because it's the first comprehensive look at what actually happened across six years and billions of doses. That's the evidence base for everything that comes next—including cancer treatment. You need to know the technology is safe before you start betting on it for other diseases.
The heart inflammation side-effect sounds serious. Why isn't that the headline?
It is serious, but it's also rare and milder than what COVID itself does to the heart. The review's point is that you have to measure risk against risk, not risk against zero. That's harder to communicate but more honest.
So this is really about cancer treatment, isn't it? That's the future.
It's the next frontier, yes. But you can't get there without proving the platform works and is safe. The COVID vaccines were the proof of concept at scale. Now oncologists can say, "We know this works. Let's try it on tumors."
How personalized are these cancer vaccines? Are they expensive?
Completely personalized—each one is built from that patient's specific tumor mutations. The source doesn't say anything about cost, but you can imagine it's not cheap. That's a question still being worked out in the trials.
What happens if the cancer comes back anyway?
That's what the trials are measuring. The logic is sound—train your immune system to recognize cancer cells and it should catch them. But cancer is clever. That's why they're testing it carefully.