Trial: mRNA-1769-P101 Mpox mPower

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

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.

While there are current efforts to protect against the virus, there is no vaccine specifically created for mpox.

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 

Check your eligibility

We’ll check to see if you may qualify for this clinical trial by asking you some questions. Additional screening will be required to determine whether you may qualify. 



What to expect

Participation in the mPower Trial will last approximately 13–14 months and includes 9 visits to a trial site at Lakeside Research in Corby 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 at Lakeside Research in Corby, 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 (FAQ) 

What is mpox?

Mpox (previously referred to as monkeypox) is the disease caused by the mpox virus. Mpox causes flu like symptoms, including fever and chills, as well as a rash with pus-filled blisters. However, not all people with mpox show symptoms. According to the World Health Organization (WHO), since May 2022, cases of mpox have been reported in countries where the virus does not normally exist, including Europe and North America.

What is a clinical trial? 

Clinical trials are carefully controlled scientific studies that evaluate how well investigational medicines may treat or prevent diseases in people. Clinical trials are conducted to answer questions such as:

  • Is the investigational treatment or vaccine safe enough to outweigh the risks? 
  • What is the best dose needed for the investigational treatment or vaccine to work? 
  • How often should the investigational treatment or vaccine be given? 
  • How effective is the investigational treatment or vaccine at treating or preventing symptoms or the condition? 

A clinical trial follows a protocol that has been approved by regulatory agencies to ensure patients’ and trial participants’ safety. The protocol outlines the types of trial participants to include, the schedule of visits and procedures, safety precautions, and what and how data will be analysed.

What are the phases of clinical trials?

Clinical trials are conducted in phases. Each phase of the trial has a different purpose and helps scientists answer different questions: 

  •  In Phase 1 trials, researchers test a new vaccine, medicine or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. 
  • In Phase 2 trials, the investigational vaccine, medicine or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety. 
  • In Phase 3 trials, the investigational vaccine, medicine or treatment is given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the medicine or treatment to be used safely. 
  • In Phase 4 trials, post marketing studies delineate additional information including the medicine’s risks, benefits and optimal use. 

Clinical Trial FAQs - Learn the Basics about Clinical Research

Why is diversity important in clinical trials? 

Clinical trials and trial volunteers are vital to advancing research of an investigational vaccine that may potentially protect people of all ages and from all backgrounds. 

Given that different populations and ages can respond differently to medical therapies, it is extremely important that this clinical trial include people of all ages, sexes, races and ethnicities to ensure the investigational vaccine is safe and effective for everyone to use.

Will compensation for time be available as part of this clinical trial?

Qualified participants will receive payment for their trial-related time and travel.

Does the mRNA-1769 investigational vaccine contain a live virus?

Often vaccines for viruses are made from a weakened or inactive (not live) virus, but the mRNA-1769 investigational vaccine is different. It is made from an instructional molecule called mRNA. mRNA makes a protein inside your cells that mimics part of the virus, triggering the body’s immune system to create antibodies. Through this natural process, it is hoped that the immune system can create the antibodies it needs to fight the real mpox virus if it is ever encountered. You cannot get mpox from the mRNA-1769 investigational vaccine.

How can I check to see if I am eligible for this trial? 

You can check if you are potentially eligible for this trial by getting in contact with us

Can I remove myself from the trial at any time? 

Participation is voluntary. You have the right to end your participation in the clinical trial at any time for any reason, or no reason at all. The clinical trial doctor or sponsor also has the right to discontinue a participant at any time for that person’s safety or if the participant no longer meets the trial requirements.

Published: Apr 3, 2024