For decades, the idea of a vaccine being injected to fight cancer sounded more like science fiction than medicine.

Fast forward to 2026 and finally, that idea may be becoming reality.

Last week, Merck & Co. and Moderna announced positive Phase 3 results for a personalised mRNA vaccine designed to help stop melanoma from returning after surgery. The announcement sent Moderna's share price soaring and reignited excitement around mRNA technology.1

Cancer vaccines have arrived. That is exciting, but the more interesting story is whether investors are getting ahead of themselves.

Cancer Treatment Gets Personal

Melanoma is a type of skin cancer. In some patients, surgery can remove the visible tumour, but tiny amounts of cancer may remain in the body and later cause the disease to return.

This is where Merck and Moderna's treatment comes in.

The vaccine, called intismeran autogene, is not a standard "one-size-fits-all" vaccine like those used against flu or COVID-19. Instead, it is designed specifically for each patient's cancer.

Doctors analyse the tumour to find unusual features that distinguish the cancer from healthy cells. The vaccine then uses mRNA, the same underlying technology that made Moderna famous during COVID-19, to teach the immune system to recognise those features and attack cancer cells.

The idea is simple: make it easier for the immune system to find the cancer cells.

And the results so far are significant.

The Phase 3 trial involved 1,137 people with high-risk melanoma. The trial met its main goal, showing that patients receiving the personalised vaccine alongside Merck's Keytruda went longer without their cancer returning than those receiving Keytruda alone.2

Keytruda (pembrolizumab): is an immunotherapy that works by blocking PD-1, a protein that acts as a brake on the immune system. Releasing that brake helps the body's own immune cells find and attack cancer cells, and Keytruda is now approved across a long list of different cancers.3

Why Are Investors Excited?

The commercial opportunity is enormous.

Merck already sells Keytruda, one of the world's most widely used cancer drugs. Adding a personalised vaccine could make the treatment more effective while creating another major revenue opportunity.

For Moderna, the stakes are even higher.

The company had enormous success during COVID-19. It became a corporate superstar during the pandemic because it had a programmable mRNA platform. That platform allowed it to move from selecting its vaccine sequence, two days after the SARS-CoV-2 genome was shared in January 2020, to delivering the first clinical batch of its COVID-19 vaccine candidate (mRNA-1273) in just 42 days.4

But this created a problem. What comes next?

As the demand for COVID vaccines fell, its share price followed. A successful cancer vaccine gives investors a reason to believe Moderna's mRNA platform is much bigger than COVID-19.

Investors are not just buying into the idea of a melanoma treatment.

They are buying into the possibility of an entirely new type of cancer medicine.

And this is where things become uncomfortable.

The Science Was Hard, The Business Is Harder

A normal drug can be mass produced millions of times and shipped globally.

This vaccine is different.

Every patient's cancer is different. The patient's tumour needs to be analysed, the relevant mutations identified, and a vaccine designed and manufactured for that individual.

Think of it as ordering a tailored suit made to measure rather than buying one off the rack.

The treatment is undeniably exciting, but potentially much harder and more expensive to produce at scale.

If producing a vaccine for a patient takes too long, it could be a serious problem.

If it costs too much, healthcare systems may struggle to pay for it. And if the treatment requires specialist facilities and complicated logistics, delivering the vaccine to thousands, or potentially millions, of patients suddenly looks far less practical.

The important question may therefore not be, "Does it work?"

But, "Can we actually deliver this to enough people?"

The Headline Has Limits

Merck and Moderna have announced that though the trial has met its key targets, the full Phase 3 results have not been released yet.5

We do not have the complete picture of how long the benefit lasts or whether it ultimately helps patients live longer.

This distinction matters.

Recurrence-free survival (RFS): the time from the start of treatment until the cancer returns or the patient dies from any cause. It is not the same as Overall Survival (OS), which measures how long patients actually live. A treatment can improve RFS long before there is evidence that it extends life.

A treatment that delays cancer returning is valuable. A treatment that prevents patients from dying from cancer is potentially transformative.

Investors must therefore decide before all the evidence is available.

The Bigger Bet

The companies are also testing the technology in other cancers, including lung, bladder and kidney cancer.6

If the same approach works across multiple cancers, the economics change completely.

Moderna would no longer have a vaccine for one type of cancer. It could have an entire platform for personalised treatment in oncology.

Merck would also use the vaccine alongside the already global Keytruda, potentially extending the value of one of the most important drugs in cancer treatment.

That is the future investors are trying to price today.

Pricing it is already proving volatile. Moderna's shares have given back a substantial part of the initial jump, closing at $142.77 on 27th August. The following day the company priced a $2.6bn issue of convertible notes, upsized from the $2.0bn it had proposed 24 hours earlier. Moderna said the proceeds were for general corporate purposes, and might include investing in the growth of its oncology business.7

Raising money on the back of a share price that has more than doubled is not a sign the science has failed. It is a reminder that building a platform is expensive, and that the bill arrives long before the revenue does.

Final Thoughts

There is no doubt this is a massive moment for cancer treatment.

Now everyone across the healthcare ecosystem (researchers, pharmaceutical companies, governments, investors and clinicians) needs to recognise there is no time to waste.

The challenge is turning this breakthrough into something patients can access. Whether that means government funding, healthcare investments, or new ways of bringing down the cost of personalised treatment, we need to find a way through.

We do not know exactly how we will get there yet. But if this is really the beginning of a new era in cancer treatment, this is the moment to push forward.

Footnotes

  1. Forbes, Moderna Shares Skyrocket 125% Toward Best Day Ever—On Success Of Cancer Drug Trial (opens in a new tab), 19th August 2026.

  2. Moderna, Merck and Moderna Announce Phase 3 INTerpath-001 Trial of Intismeran Autogene Plus KEYTRUDA Met Endpoints of Recurrence-Free Survival (RFS) and Distant Metastasis-Free Survival (DMFS) in Patients With Completely Resected Stage IIB-IV Melanoma (opens in a new tab), 19th August 2026.

  3. DailyMed, KEYTRUDA (pembrolizumab) injection, for intravenous use (opens in a new tab), 10th July 2026.

  4. Moderna, Moderna Ships mRNA Vaccine Against Novel Coronavirus (mRNA-1273) for Phase 1 Study (opens in a new tab), 24th February 2020.

  5. NBC News, Merck and Moderna say cancer vaccine shows promise in preventing recurrence of melanoma (opens in a new tab), 19th August 2026.

  6. The ASCO Post, INTerpath-001 Trial of mRNA-Based Individualized Neoantigen Therapy Meets Primary and Key Secondary Endpoints in Patients With High-Risk Resected Melanoma (opens in a new tab), 21st August 2026.

  7. Moderna, Moderna Announces Pricing of Upsized $2.6 Billion Offering of Convertible Senior Notes (opens in a new tab), 28th August 2026.