| E.1 Medical condition or disease under investigation | 
| E.1.1 | Medical condition(s) being investigated | 
| Fibrodyplasia Ossificans Progressiva (FOP) |  | 
| E.1.1.1 | Medical condition in easily understood language | 
| Genetic condition which causes abnormal formation of bone at abnormal locations such as in the muscles, tendons and ligaments.
 |  | 
| E.1.1.2 | Therapeutic area | Diseases [C] - Musculoskeletal Diseases [C05] | 
| MedDRA Classification | 
| E.1.2 Medical condition or disease under investigation | 
| 
| E.1.2 | Version | 20.0 |  
| E.1.2 | Level | PT |  
| E.1.2 | Classification code | 10068715 |  
| E.1.2 | Term | Fibrodysplasia ossificans progressiva |  
| E.1.2 | System Organ Class | 10010331 - Congenital, familial and genetic disorders |  | 
| E.1.3 | Condition being studied is a rare disease | Yes | 
| E.2 Objective of the trial | 
| E.2.1 | Main objective of the trial | 
| To describe and investigate safety and tolerability of the intradermal delivery of two fractional doses of 20 μg mRNA-1273 in patients with Fibrodysplasia Ossificans Progressiva. |  | 
| E.2.2 | Secondary objectives of the trial | 
| To compare the immunogenicity of patients with FOP after intradermal delivery of two fractional doses of 20 μg mRNA-1273 with that of two doses of 20 μg mRNA-1273 vaccine through intramuscular delivery and intradermal delivery on Day 43,  as previously investigated in LUMC cohort of healthy adults |  | 
| E.2.3 | Trial contains a sub-study | No | 
| E.3 | Principal inclusion criteria | 
| In order to be eligible to participate in this study, a subject must meet all of the following criteria: •	Fibrodysplasia ossificans progressiva as determined by confirmation of any causative genetic mutation in the ACVR1 gene as previously described (1).
 •	18 years or older
 •	Participants who are willing and able to comply with all scheduled visits, vaccination tests and other study procedure
 •	Capable of giving personal signed consent as described in appendix 1, which includes compliance with the requirements and restrictions listed in the ICD and this protocol
 •	Females only: female volunteers of childbearing potential (i.e. have a uterus and are neither surgically sterilised nor post-menopausal) must not be pregnant or breastfeeding. They should agree to use adequate contraception at least up to four weeks following the final dose of mRNA-1273 vaccine.
 
 |  | 
| E.4 | Principal exclusion criteria | 
| A potential subject who meets any of the following criteria will be excluded from participation in this study: •	History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s).
 •	Receipt of medications intended to prevent SARS-CoV-2 infection.
 •	Current clinical complaints consistent with SARS-CoV-2 infection (three or more of the following complaints: headache, loss of smell, sore throat, hoarseness, cough, chest pain, shortness of breath, fatigue, diarrhea, fever).
 •	SARS-CoV-2 vaccination 6 months prior to participation.
 •	Immunosuppressed individuals with known or suspected immunodeficiency, as determined by history.
 •	Individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention.
 •	Women who are pregnant or breastfeeding.
 •	Planned pregnancy within four weeks after the final injection.
 •	SARS-CoV-2 PCR-positive EMA approved lateral flow test at the screening before receipt of fist vaccine dose
 •	Receipt of any other non-study vaccine within 28 days, before first study dose.
 •	Anticipated receipt of any other non-study vaccine within 28 days, after last study dose administration.
 |  | 
| E.5 End points | 
| E.5.1 | Primary end point(s) | 
| •	Nature, frequency and severity of local reactions. Solicited adverse events include: pain, redness and swelling at the injection site and pain and swelling at the regional lymph nodes •	Nature, frequency and severity of systemic events. Solicited adverse events include: flare-up, fever, fatigue, headache, chills, vomiting, diarrhoea, new or worsened muscle pain, and new or worsened joint pain.
 •	Use of corticosteroids, antipyretics and painkillers
 
 |  | 
| E.5.1.1 | Timepoint(s) of evaluation of this end point |  | 
| E.5.2 | Secondary end point(s) | 
| •	SARS-CoV 2 WT neutralising antibody titres rate on Day 1 and Day 43 •	SARS-CoV-2-spike protein–specific binding IgG level on Day 1 and Day 43
 •	B-cell and T-cell responses on day 1 and day 43
 
 |  | 
| E.5.2.1 | Timepoint(s) of evaluation of this end point |  | 
| E.6 and E.7 Scope of the trial | 
| E.6 | Scope of the trial | 
| E.6.1 | Diagnosis | No | 
| E.6.2 | Prophylaxis | Yes | 
| E.6.3 | Therapy | No | 
| E.6.4 | Safety | Yes | 
| E.6.5 | Efficacy | No | 
| E.6.6 | Pharmacokinetic | No | 
| E.6.7 | Pharmacodynamic | No | 
| E.6.8 | Bioequivalence | No | 
| E.6.9 | Dose response | No | 
| E.6.10 | Pharmacogenetic | No | 
| E.6.11 | Pharmacogenomic | No | 
| E.6.12 | Pharmacoeconomic | No | 
| E.6.13 | Others | No | 
| E.7 | Trial type and phase | 
| E.7.1 | Human pharmacology (Phase I) | No | 
| E.7.1.1 | First administration to humans | No | 
| E.7.1.2 | Bioequivalence study | No | 
| E.7.1.3 | Other | No | 
| E.7.1.3.1 | Other trial type description |  | 
| E.7.2 | Therapeutic exploratory (Phase II) | Yes | 
| E.7.3 | Therapeutic confirmatory (Phase III) | No | 
| E.7.4 | Therapeutic use (Phase IV) | No | 
| E.8 Design of the trial | 
| E.8.1 | Controlled | No | 
| E.8.1.1 | Randomised | No | 
| E.8.1.2 | Open | Yes | 
| E.8.1.3 | Single blind | No | 
| E.8.1.4 | Double blind | No | 
| E.8.1.5 | Parallel group | No | 
| E.8.1.6 | Cross over | No | 
| E.8.1.7 | Other | No | 
| E.8.2 | Comparator of controlled trial | 
| E.8.2.1 | Other medicinal product(s) | No | 
| E.8.2.2 | Placebo | No | 
| E.8.2.3 | Other | No | 
| E.8.3 | The trial involves single site in the Member State concerned | Yes | 
| E.8.4 | The trial involves multiple sites in the Member State concerned | No | 
| E.8.5 | The trial involves multiple Member States | No | 
| E.8.6 Trial involving sites outside the EEA | 
| E.8.6.1 | Trial being conducted both within and outside the EEA | No | 
| E.8.6.2 | Trial being conducted completely outside of the EEA | No | 
| E.8.7 | Trial has a data monitoring committee | No | 
| E.8.8 | Definition of the end of the trial and justification where it is not the last
                        visit of the last subject undergoing the trial |  | 
| E.8.9 Initial estimate of the duration of the trial | 
| E.8.9.1 | In the Member State concerned years | 0 | 
| E.8.9.1 | In the Member State concerned months | 6 | 
| E.8.9.1 | In the Member State concerned days | 0 | 
| E.8.9.2 | In all countries concerned by the trial years | 0 | 
| E.8.9.2 | In all countries concerned by the trial months | 6 | 
| E.8.9.2 | In all countries concerned by the trial days | 0 |