1. past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of multisystem inflammatory syndrome in children (mis-c). 2. participants with active graft-vs-host disease (gvhd), transplant rejection, or posttransplant lymphoproliferative disorder (ptld), or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants \<18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. 10. previous vaccination with any coronavirus vaccine. 11. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. 12. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 13. previous participation in other studies involving study intervention containing lipid nanoparticle (lnps). 14. participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 15. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

1. past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of multisystem inflammatory syndrome in children (mis-c). 2. participants with active graft-vs-host disease (gvhd), transplant rejection, or posttransplant lymphoproliferative disorder (ptld), or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants \<18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. 10. previous vaccination with any coronavirus vaccine. 11. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. 12. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 13. previous participation in other studies involving study intervention containing lipid nanoparticle (lnps). 14. participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 15. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of multisystem inflammatory syndrome in children (mis-c). participants with active graft-vs-host disease (gvhd), transplant rejection, or posttransplant lymphoproliferative disorder (ptld), or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. participant who is pregnant or breastfeeding. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. previous vaccination with any coronavirus vaccine. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. previous participation in other studies involving study intervention containing lipid nanoparticle (lnps). participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of multisystem inflammatory syndrome in children (mis-c). participants with active graft-vs-host disease (gvhd), transplant rejection, or posttransplant lymphoproliferative disorder (ptld), or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. participant who is pregnant or breastfeeding. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. previous vaccination with any coronavirus vaccine. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. previous participation in other studies involving study intervention containing lipid nanoparticle (lnps). participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of mis-c. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. participant who is pregnant or breastfeeding. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. previous vaccination with any coronavirus vaccine. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. previous participation in other studies involving study intervention containing lnps. participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

past clinical (based on covid-19 symptoms/signs alone, if a sars-cov-2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid-19, or a past clinical diagnosis of mis-c. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. participant who is pregnant or breastfeeding. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. previous vaccination with any coronavirus vaccine. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 4. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. previous participation in other studies involving study intervention containing lnps. participants who are direct descendants (child or grandchild) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

- 1. past clinical (based on covid-19 symptoms/signs alone, if a sars cov 2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid 19, or a past clinical diagnosis of mis-c. 2. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. 10. previous vaccination with any coronavirus vaccine. 11. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 3. 12. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 13. previous participation in other studies involving study intervention containing lnps. 14. participants who are direct descendants (child or grandchild, parent or grandparent) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 15. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

- 1. past clinical (based on covid-19 symptoms/signs alone, if a sars cov 2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid 19, or a past clinical diagnosis of mis-c. 2. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. participants who do not have adequate deltoid muscle mass to allow intramuscular vaccination, in the opinion of the investigator. 10. previous vaccination with any coronavirus vaccine. 11. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 3. 12. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 13. previous participation in other studies involving study intervention containing lnps. 14. participants who are direct descendants (child or grandchild, parent or grandparent) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 15. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

- 1. past clinical (based on covid-19 symptoms/signs alone, if a sars cov 2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid 19, or a past clinical diagnosis of mis-c. 2. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. previous vaccination with any coronavirus vaccine. 10. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 3. 11. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 12. previous participation in other studies involving study intervention containing lnps. 13. participants who are direct descendants (child or grandchild, parent or grandparent) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 14. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

- 1. past clinical (based on covid-19 symptoms/signs alone, if a sars cov 2 naat result was not available) or microbiological (based on covid-19 symptoms/signs and a positive sars-cov-2 naat result) diagnosis of covid 19, or a past clinical diagnosis of mis-c. 2. participants with active gvhd, transplant rejection, or ptld, or participants who have had treatment for these conditions within 3 months (84 days) prior to study enrollment (visit 1). 3. participants <18 years of age whose weight is less than the 5th percentile of age-adjusted ideal body weight. 4. other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. 5. history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). 6. bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. 7. participant who is pregnant or breastfeeding. 8. participants who may be ineligible because of the number of phlebotomy assessments during this study, in the opinion of the investigator. 9. previous vaccination with any coronavirus vaccine. 10. ongoing, or history of, treatment with blood/plasma products or immunoglobulins within 3 months (84 days) prior to dose 1 or planned receipt of these medications prior to dose 3. 11. participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation. 12. previous participation in other studies involving study intervention containing lnps. 13. participants who are direct descendants (child or grandchild, parent or grandparent) of investigational site staff members or pfizer/biontech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members. 14. investigator site staff or pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.