Moderna and Merck have reported that their individualised cancer vaccine met its main goal of preventing melanoma from returning, and a secondary goal of stopping it spreading elsewhere in the body. Moderna's shares nearly tripled, adding roughly $44 billion of market value.

Both halves of that sentence are worth taking seriously, and they are not the same kind of statement.

What an individualised neoantigen vaccine is

It is not a vaccine in the ordinary sense. A conventional vaccine presents the immune system with a fragment of a pathogen that is the same in everybody.

This one starts with a biopsy. The patient's tumour is sequenced, and the mutations present in the cancer but not in the patient's healthy tissue are identified. Those mutations produce proteins the immune system has never been trained on, which are called neoantigens. Software selects a set of them, and an mRNA sequence encoding those targets is manufactured for that one person and given alongside Merck's Keytruda, an immunotherapy that releases a brake on the immune response.

The logic is that Keytruda lets the immune system attack, and the vaccine tells it what to attack. Every dose is a different product, made for a single patient, which is why this is an industrial problem as much as a biological one.

What has actually been released

Very little, which is the part investors should hold in mind.

The companies say both endpoints were met. The figure in circulation, a 44% reduction in the risk of recurrence or death against Keytruda alone, comes from earlier results rather than from this readout. The current announcement does not include the patient count, does not state the trial phase, does not give a hazard ratio or confidence interval, does not say how long patients were followed, and does not report whether the effect held across subgroups or what adverse events occurred.

Detailed results are promised at a medical conference later this year, and the companies are aiming at US approval next year.

None of that means the result is weak. Topline announcements ahead of conference presentations are routine, and companies are constrained in what they can say before a trial is published. It means the market has repriced a company by $44 billion on a claim that cannot yet be independently assessed, and the assessment arrives later.

Why it matters this much to Moderna

Because there is not much else. Moderna's revenue collapsed once Covid vaccine demand fell away, the shares fell a long way from their pandemic peak, and the company has been cutting costs since. The cancer programme has been the main reason to own the stock rather than one line in a diversified pipeline.

That concentration is what produces a tripling on one announcement. It also means the downside if the detailed data disappoints is proportionate.

The economics nobody has explained yet

Chief executive Stéphane Bancel has said an approved treatment would cost less than CAR-T therapies, which run to about $500,000 a patient. That is a ceiling rather than a price, and it points at the real question.

A therapy manufactured individually for each patient has no manufacturing scale in the ordinary sense. Sequencing, target selection, synthesis, quality control and release testing happen per person, on a clock, because the patient is waiting. Whether that can be done at a price health systems will pay, and at a throughput that reaches more than a few thousand people a year, is a separate problem from whether the biology works, and it is not solved by a positive trial.

What to watch

The conference presentation, and specifically the hazard ratio, the confidence interval and the length of follow-up. Whether the regulatory filing seeks accelerated approval or a standard review. And the results from the same platform in lung, kidney and pancreatic cancers, where nothing has been reported, because melanoma is unusually visible to the immune system and success there has historically not transferred easily to other tumours.

This is reporting on a clinical announcement and a market reaction, not a view on the stock or on any treatment decision.