Inclusion Criteria:  Aged 18-30 years on proposed date of enrolment. Body Mass Index (BMI) ≥18.5 kg/m2and ≤28 kg/m2. In good health with no history of clinically significant medical conditions (as described in Exclusion criteria) that would interfere with subject safety, as defined by medical history, physical examination, routine laboratory tests, cardiovascular magnetic resonance imaging or echocardiogram, ECG, pulmonary function tests and Chest X-Ray as determined by the Investigator at a screening evaluation. Volunteer is willing and able to give written informed consent for participation in the study Willing to allow the investigators to discuss the volunteer's medical history with their General Practitioner or any relevant health authority Allow the investigator to register volunteer details with a confidential database (The Over-volunteering Prevention Service) to prevent concurrent entry into clinical studies/trials Agreement to refrain from blood donation during the course of the study a. For women of child bearing potential (WOCBP), a willingness to practice continuous effective contraception during the study and, a negative pregnancy test on the day(s) of screening and challenge b. For men, a willingness to practice continuous effective contraception (see below) from day of challenge to 6 months post treatment with Regeneron Able and willing (in the investigator's opinion) to comply with all study requirements No clinically relevant findings in medical history or on physical examination For Groups 1 & 2: Previous microbiological confirmation of SARS-CoV-2 infection >3 months prior to enrolment (proof of positive PCR confirmed via medical notes/or PHE) For Groups 3 & 4: Written or electronic evidence of at least one vaccination against SARS- CoV-2 >21 days prior to enrolment (proof required would include written or electronic evidence from GP/ medical records or electronic NHS COVID pass).  Exclusion Criteria:  1) History or evidence of any clinically significant or currently active cardiovascular, (including thromboembolic events), respiratory (excluding SARS CoV-2 infection), dermatological, gastrointestinal, endocrine, haematological, hepatic, immunological, rheumatological, metabolic, urological, renal, neurological or psychiatric illness. Specifically:  Volunteers with any history of physician diagnosed and/or objective test confirmed asthma, chronic obstructive pulmonary disease, pulmonary hypertension, reactive airway disease, or chronic lung condition of any aetiology or who have experienced:  i) Significant/severe wheeze in the past ii) Respiratory symptoms including wheeze which has ever resulted in hospitalisation iii) Known bronchial hyper reactivity to viruses  History of thromboembolic, cardiovascular or cerebrovascular disease History or evidence of diabetes mellitus (Type I or Type II) Any concurrent serious illness including history of malignancy that could interfere with the aims of the study or a subject completing the study. Basal cell carcinoma within 5 years of treatment or with evidence of recurrence is also an exclusion. Migraine with associated neurological symptoms such as hemiplegia or vision loss. Cluster headache/migraine or prophylactic treatment for migraine History or evidence of autoimmune disease or known immunodeficiency of any cause (including HIV). Psychiatric illness including volunteers with a history of depression and/or anxiety with associated severe psychiatric comorbidities, for example psychosis. Specifically, i) Volunteers with history of anxiety-related symptoms of any severity within the last 2 years if the Generalized Anxiety Disorder-7 score is ≥5 ii) Volunteers with a history of depression of any severity within the last 2 years if the Patient Health Questionnaire-9 score is ≥4 iii) Significant claustrophobia Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following injections or venepuncture. Other major disease that, in the opinion of the Investigator, could interfere with a subject completing the study and necessary investigations.  2) Clinically significant smoking history. Defined as: Current smoker (any smoking including e-cigarettes in the last 3 months) or > 2 pack year smoking history at any time (2 pack years is equivalent to 20 cigarettes daily for 2 years), or use of any nicotine containing products within the last 3 months.  3) History or presence of alcohol addiction, or excessive use of alcohol (average weekly intake in excess of 28 units alcohol; one unit being a half glass of beer, a small glass of wine or a measure of spirits)  4) Clinically significant history of use of drugs of misuse, with evidence of a negative drugs of misuse urine test required at screening and quarantine admission  5) History of anaphylaxis or any allergy likely to be worsened by any component of the study agent or proposed treatment regime.  6) Clinically active rhinitis (including hay fever) or history of moderate to severe rhinitis, or history of seasonal allergic rhinitis likely to be active at time of inclusion into the study and/or requiring regular nasal corticosteroids on at least weekly basis, within 30 days of admission to quarantine.  7) Any significant abnormality altering the anatomy of the nose or nasopharynx, clinically significant history of epistaxis (nose bleeds) or any nasal or sinus surgery within six months of inoculation  8) Clinical, radiological, or laboratory evidence of current active TB disease or latent TB infection  9) Previous VZV pneumonia  10) Positive HBsAg, HCV or HIV antibodies  11) Concurrent use of oral, inhaled or systemic steroid medication or use within the last 6 months (steroids used as a cream or ointment are permissible), or the use of other immunosuppressive agents concurrently or within the last 6 months.  12) Administration of immunoglobulins and/or any blood products within the three months preceding the planned study challenge date  13) Current use of any medication or other drug taken through the nasal or inhaled route including cocaine or other recreational drugs  14) Plans to receive a live vaccination 30 days prior to enrolment, or any vaccination (i.e. non-live, including a SARS-CoV-2 vaccine) 21 days prior to enrolment and/or plans to take any vaccination 30 days following enrolment  15) Current pregnancy or pregnancy within the last 6 months, lactation or intention to become pregnant during study period  16) Shares a household/ is in a support bubble with someone with clinically significant immunodeficiency (due to underlying medical condition, medication or pregnancy); or who is extremely clinically vulnerable as per Public Health England guidelines  17) Participation in another research study involving receipt of an investigational product in the 30 days preceding enrolment, or planned use during the study period  18) Laboratory confirmed (PCR or lateral flow antigen test) SARS-Cov-2 infection, evidence of viral pneumonitis on chest radiograph or a high clinical suspicion of COVID-19 disease in the 3 months preceding enrolment.  19) Post COVID-19 symptoms that have not resolved by 1 month prior to enrolment  20) Previous hospitalisation with COVID-19 disease or related complications e.g. pulmonary fibrosis on chest x ray  21) Family history of 1st degree relative aged 50 years or less with sudden cardiac or unexplained death  22) Family history of severe COVID-19 disease or response to any other viral disease e.g. Guillain-Barré  23) Family history unavailable or in opinion of investigators not sufficient to assess criteria 22 and 23.  24) Clinically significant abnormality on screening chest radiograph  25) Clinically significant abnormality of lung function testing  26) Clinically significant structural heart disease detected on CMR or echocardiogram, such as abnormal ventricular systolic function, evidence of previous myocardial infarction, previous myocarditis (on CMR) or significant valvular heart disease (more than mild)  27) Any clinically significant abnormality of screening blood or urine tests  28) Any other significant disease, disorder, or finding, which, in the opinion of the investigator, may either put the volunteer at risk, affect the volunteer's ability to participate in the study or impair interpretation of the study data  29) Venous access deemed inadequate for the phlebotomy and cannulation demands of the study.  For Groups 3 & 4:  Previous positive test for SARS CoV-2 infection (PCR or lateral flow antigen test) or a high clinical suspicion of COVID-19 disease at any time. Positive Anti-nucleocapsid IgG at screening, unless explainable by vaccination