Unable to provide written, informed consent Participation in any other interventional trials People who have already received a booster vaccination Any significant or uncontrolled disease posing a risk with vaccination as judged by the investigator Any significant medical condition that in the opinion of the investigator would necessitate booster vaccination against SARS-CoV-2 within the trial timelines Any kind of dependency on the sponsor or principal investigator or employed by the sponsor or principal investigator Where a subject’s primary vaccination and third dose vaccination was not with the BNT162b2 mRNA vaccine Any contraindication to the vaccines in the trial as per the Summary of Medicinal Product Characteristics, SmPC) or the Investigator’s Brochure, if appropriate. Use of drugs with significant interaction with the investigational product Subjects who are pregnant and who are planning to become pregnant Nursing mothers Unwillingness to use highly effective contraceptive methods.

Unable to provide written, informed consent Participation in any other interventional trials People who have already received a booster vaccination Any significant or uncontrolled disease posing a risk with vaccination as judged by the investigator Any significant medical condition that in the opinion of the investigator would necessitate booster vaccination against SARS-CoV-2 within the trial timelines Any kind of dependency on the sponsor or principal investigator or employed by the sponsor or principal investigator Where a subject’s primary vaccination and third dose vaccination was not with the BNT162b2 mRNA vaccine Any contraindication to the vaccines in the trial as per the Summary of Medicinal Product Characteristics, SmPC) or the Investigator’s Brochure, if appropriate. Use of drugs with significant interaction with the investigational product Subjects who are pregnant and who are planning to become pregnant Nursing mothers Unwillingness to use highly effective contraceptive methods.

-Unable to provide written, informed consent -Participation in any other interventional trials -People who have already received a booster vaccination -Any significant or uncontrolled disease posing a risk with vaccination as judged by the investigator (including recent, confirmed positive SARS-CoV-2 test within the previous three weeks) - Any significant medical condition that in the opinion of the investigator would necessitate booster vaccination against SARS-CoV-2 within the trial timelines - Any kind of dependency on the principal investigator or employed by the sponsor or principal investigator -Where a subject received primary vaccination not with two doses of the BNT162b2 mRNA vaccine or the primary vaccination was with two different vaccine products as 1st and 2nd vaccination doses (heterologous vaccination scheme) -Any contraindication to the vaccines in the trial at the moment of randomization as per the Summary of Medicinal Product Characteristics, SmPC) or the Investigator’s Brochure, if appropriate. A list of contraindications (including prior anaphylaxis to BNT162b2) are listed in Annex A. -Use of drugs with significant interaction with the investigational product -Subjects who are pregnant -Unwillingness to use highly effective contraceptive methods. The following contraceptive methods with a Pearl Index lower than 1% are regarded as highly-effective: o Oral hormonal contraception o Dermal hormonal contraception o Vaginal hormonal contraception (NuvaRing®) o Contraceptive plaster o Long-acting injectable contraceptives o Implants that release progesterone (Implanon®) o Tubal ligation (female sterilisation) o Intrauterine devices that release hormones (hormone spiral) o Double barrier methods

-Unable to provide written, informed consent -Participation in any other interventional trials -People who have already received a booster vaccination -Any significant or uncontrolled disease posing a risk with vaccination as judged by the investigator (including recent, confirmed positive SARS-CoV-2 test within the previous three weeks) - Any significant medical condition that in the opinion of the investigator would necessitate booster vaccination against SARS-CoV-2 within the trial timelines - Any kind of dependency on the principal investigator or employed by the sponsor or principal investigator -Where a subject received primary vaccination not with two doses of the BNT162b2 mRNA vaccine or the primary vaccination was with two different vaccine products as 1st and 2nd vaccination doses (heterologous vaccination scheme) -Any contraindication to the vaccines in the trial at the moment of randomization as per the Summary of Medicinal Product Characteristics, SmPC) or the Investigator’s Brochure, if appropriate. A list of contraindications (including prior anaphylaxis to BNT162b2) are listed in Annex A. -Use of drugs with significant interaction with the investigational product -Subjects who are pregnant -Unwillingness to use highly effective contraceptive methods. The following contraceptive methods with a Pearl Index lower than 1% are regarded as highly-effective: o Oral hormonal contraception o Dermal hormonal contraception o Vaginal hormonal contraception (NuvaRing®) o Contraceptive plaster o Long-acting injectable contraceptives o Implants that release progesterone (Implanon®) o Tubal ligation (female sterilisation) o Intrauterine devices that release hormones (hormone spiral) o Double barrier methods