inclusion criteria: * adults from 18 to 55 years of age * adults aged 56-69 years old (after review of safety data by dsmb in this age group in the uk trial) * adults aged 70 and above years old (after review of safety data by dsmb in this age group in the uk trial) * able and willing (in the investigator's opinion) to fulfill all study requirements; * health professionals and adults at high risk of exposure to sars-cov-2, as defined in section 5.2 of this protocol; * serology with sars-cov-2 negative igg antibodies; this inclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards. * willing to allow investigators to discuss the participant's clinical history with their gp/personal physician and access medical records relevant to the study procedures * only for women of childbearing age willing to practice continuous effective birth control (see below) during the study, and a negative pregnancy test on the screening and vaccination day(s); * consent to abstain from blood donation during the course of the study; * provide informed consent in writing

inclusion criteria: * adults from 18 to 55 years of age * adults aged 56-69 years old (after review of safety data by dsmb in this age group in the uk trial) * adults aged 70 and above years old (after review of safety data by dsmb in this age group in the uk trial) * able and willing (in the investigator's opinion) to fulfill all study requirements; * health professionals and adults at high risk of exposure to sars-cov-2, as defined in section 5.2 of this protocol; * serology with sars-cov-2 negative igg antibodies; this inclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards. * willing to allow investigators to discuss the participant's clinical history with their gp/personal physician and access medical records relevant to the study procedures * only for women of childbearing age willing to practice continuous effective birth control (see below) during the study, and a negative pregnancy test on the screening and vaccination day(s); * consent to abstain from blood donation during the course of the study; * provide informed consent in writing

inclusion criteria: - adults from 18 to 55 years of age - adults aged 56-69 years old (after review of safety data by dsmb in this age group in the uk trial) - adults aged 70 and above years old (after review of safety data by dsmb in this age group in the uk trial) - able and willing (in the investigator's opinion) to fulfill all study requirements; - health professionals and adults at high risk of exposure to sars-cov-2, as defined in section 5.2 of this protocol; - serology with sars-cov-2 negative igg antibodies; this inclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards. - willing to allow investigators to discuss the participant's clinical history with their gp/personal physician and access medical records relevant to the study procedures - only for women of childbearing age willing to practice continuous effective birth control (see below) during the study, and a negative pregnancy test on the screening and vaccination day(s); - consent to abstain from blood donation during the course of the study; - provide informed consent in writing

inclusion criteria: - adults from 18 to 55 years of age - adults aged 56-69 years old (after review of safety data by dsmb in this age group in the uk trial) - adults aged 70 and above years old (after review of safety data by dsmb in this age group in the uk trial) - able and willing (in the investigator's opinion) to fulfill all study requirements; - health professionals and adults at high risk of exposure to sars-cov-2, as defined in section 5.2 of this protocol; - serology with sars-cov-2 negative igg antibodies; this inclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards. - willing to allow investigators to discuss the participant's clinical history with their gp/personal physician and access medical records relevant to the study procedures - only for women of childbearing age willing to practice continuous effective birth control (see below) during the study, and a negative pregnancy test on the screening and vaccination day(s); - consent to abstain from blood donation during the course of the study; - provide informed consent in writing