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This trial has completed recruitment on this platform, and is no longer accepting new referrals.

A clinical trial of an investigational mpox vaccine for adults ages 18–49

Trial ID: mRNA-1769-P101
The mPower Trial is a clinical trial conducted by Moderna to evaluate the safety of, and immune response to, an investigational vaccine called mRNA-1769, which aims to protect against illness caused by the mpox (previously called monkeypox) virus. “Investigational” means it has not been approved by the MHRA or another health regulatory authority.

Trial Details

In the mPower Trial, Moderna is evaluating whether an investigational vaccine called mRNA-1769 could protect adults against illness caused by the mpox virus.

About 350 participants will be enrolled into the mPower Trial. Participants will receive the investigational vaccine or a placebo, a saltwater solution that includes no active ingredients.

Estimated Enrolment

Approx. 350 Participants



Eligibility Criteria

Participants must:

  • Be 18–49 years of age
  • Be in generally good health

Participants must not:

  • Have previously received a smallpox or mpox vaccine
  • Have been recently exposed to mpox

Site Locations

Participants will need to go to one of the clinics taking part in this clinical trial.

Sites are located in the towns/cities identified with the red pin:

What to Expect

Participation in the mPower Trial will last approximately 13–14 months and includes 9 visits to a trial site (clinic) and up to 3 safety phone calls.

Participants will be chosen at random to receive 2 doses of the investigational vaccine or a placebo. By comparing the investigational vaccine to a placebo, medical researchers can better understand how well the investigational vaccine works. All trial participants will receive the same level of quality care regardless of whether they are assigned to the investigational vaccine or the placebo. The trial doctor will not know which option or dosage participants have been assigned, but in the case of a medical emergency, they can quickly find out.

Both the investigational vaccine and the placebo will be given as injections in the upper arm. During visits to the trial site, the trial staff will talk to participants about their health and perform medical assessments. These assessments may include taking vital signs, an electrocardiogram (ECG), and a blood sample collection.

Participants will be asked to use an electronic diary (eDiary) app on their smartphone or a provided device to report any side effects they might experience for 1 week after each injection.

Insurance is not needed to participate, and qualified participants will receive payment for their trial-related time and travel.

Frequently Asked Questions (FAQs)