Moderna and Merck: mRNA cancer vaccine against melanoma sends shares soaring

Working with Merck, Moderna is developing an mRNA vaccine for one of the most serious forms of skin cancer: melanoma. Positive early findings from the final stage of clinical trials have sent the US company’s share price soaring.

Moderna saw a spectacular stock-market rise (+88% on Wednesday), five years after the company was at the centre of attention during the Covid-19 pandemic. On 19 August 2026, the biotech firm announced encouraging initial findings from a large-scale clinical trial of the cancer vaccine it is developing alongside Merck.

Intismeran, Moderna and Merck’s mRNA melanoma vaccine

The cancer treatment, known as Intismeran, underwent its first tests in 2022. Like the Covid-19 vaccine, it uses mRNA technology. The injection is intended to achieve two aims: reducing the risk of cancer returning and preventing cancers from spreading to other parts of the body. The interim study found that the vaccine achieved both objectives.

Before Moderna became involved, Merck had already been developing a treatment. However, its therapy, called “Keytruda”, did not provide a strong recurrence-free survival result. Moderna’s work has therefore complemented Merck’s immunotherapy with personalised mRNA treatment.

1,100 patients included in the final phase of clinical trials

This treatment has now reached phase 3 of clinical testing. Should the results ultimately prove positive, Moderna and Merck will be able to bring their therapy to market. The findings remain interim, meaning detailed data on the treatment’s effectiveness have not yet been released. This decisive phase 3 trial involves 1,100 people.

If successful, it would represent the first approval of this kind for an mRNA cancer vaccine. It would mark a major advance for the use of this technology compared with conventional vaccines. For melanoma skin cancer, this “tailor-made” therapy can be adapted to the specific mutations found in each person’s tumour.

How mRNA technology works in melanoma treatment

mRNA is an injected molecule that acts as a set of instructions for the body’s cells. Once it has been administered, the body makes the required proteins, prompting the immune system to respond by producing the necessary antibodies. Contrary to what some may believe, mRNA does not “modify” our DNA: the molecule is broken down by our cells and never enters their nucleus, where DNA is located.

Moderna’s wild reaction, Merck’s more restrained one: the explanation

It took little time for the positive cancer-vaccine announcement to push Moderna shares up by almost 100%. At the same time, Merck’s share price rose by 11.2%. Two factors explain why the market reaction was so wild for one laboratory and more restrained for the other.

First, Moderna is going through a difficult period, with revenue falling after the exceptional windfall generated during the pandemic. From more than $19 million in 2022, revenue dropped to under $7 million in 2023, $3.2 million in 2024 and less than $2 million in 2025.

The second reason lies in the significance of the news. Bringing the treatment to market would have a considerable effect on Moderna’s business, as the company had no presence in this area until now. For Merck, however, the launch would simply strengthen an existing treatment that it already offers. Volumes could logically increase, but Merck already earns revenue from its therapy.