(TRIAL ONGOING) This clinical trial, that commenced on 26 April 2020, is trialling HBOT-treatment for 30 COVID-19 positive patients hospitalized with moderate and severe symptoms including respiratory distress and at least one risk factor for bad prognosis of COVID-19 i.e. hypertension, diabetes mellitus, ischemic heart disease, smoking, or age >50 etc. This is a randomized, controlled double-blinded study: Participants are unaware if they are being treated with hyperbaric or normobaric oxygen within the chamber (as they are blinded to the measured chamber pressure) and the outcome assessors receive anonymous blinded data. Each patient is receiving a total of 8 treatment sessions during a 4-day period. Outcome measures include lung oxygenation index, percentage of oxygen saturation, inflammation level, viral load in the blood, chest x-ray changes, pulmonary function tests, number of patients who developed IgM or IgG antibodies, number of adverse events per group, and recovery duration (until patient has two negative COVID-19 tests).