inclusion criteria: * previously vaccinated with comirnaty (pfizer) and/or previously contracted covid-19 at least 3 months before inclusion * healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalisation for worsening disease during the 6 weeks before enrolment, can be included. * participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. * participants are willing to postpone their regular covid-19 revaccination upon invitation by the municipal health center or general practitioner until four weeks after receiving the intervention (after the last sampling of d29). * capable of giving personal signed informed consent as described in appendix 1, which includes compliance with the requirements and restrictions listed in the icd and in this protocol.

inclusion criteria: * previously vaccinated with comirnaty (pfizer) and/or previously contracted covid-19 at least 3 months before inclusion * healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalisation for worsening disease during the 6 weeks before enrolment, can be included. * participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. * participants are willing to postpone their regular covid-19 revaccination upon invitation by the municipal health center or general practitioner until four weeks after receiving the intervention (after the last sampling of d29). * capable of giving personal signed informed consent as described in appendix 1, which includes compliance with the requirements and restrictions listed in the icd and in this protocol.

inclusion criteria: previously vaccinated with comirnaty (pfizer) and/or previously contracted covid-19 at least 3 months before inclusion healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalisation for worsening disease during the 6 weeks before enrolment, can be included. participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. participants are willing to postpone their regular covid-19 revaccination upon invitation by the municipal health center or general practitioner until four weeks after receiving the intervention (after the last sampling of d29). capable of giving personal signed informed consent as described in appendix 1, which includes compliance with the requirements and restrictions listed in the icd and in this protocol.

inclusion criteria: previously vaccinated with comirnaty (pfizer) and/or previously contracted covid-19 at least 3 months before inclusion healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalisation for worsening disease during the 6 weeks before enrolment, can be included. participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. participants are willing to postpone their regular covid-19 revaccination upon invitation by the municipal health center or general practitioner until four weeks after receiving the intervention (after the last sampling of d29). capable of giving personal signed informed consent as described in appendix 1, which includes compliance with the requirements and restrictions listed in the icd and in this protocol.