Janssen Ad26.CoV2.S Vaccine Booster in Kidney Transplant Recipients

Inclusion Criteria: Criteria for Entry into the Study: * Any kidney transplant recipient from Mayo Clinic who has received the mRNA vaccine (two or three dose mRNA vaccine-Moderna or Pfizer) and are \>28 days after most recent vaccination at the time of spike protein assessment. * Recipients of a kidney transplant, including those transplanted with other solid organ transplants in addition to the kidney. Subjects may have received more than 1 kidney transplant. * More than 90 days since any transplant including a kidney transplantation. •≥18 years of age on the day of consent. Criteria for Entry into Segment I * Must have a Roche Elecsys® Anti-SARS-CoV-2 S level of \<250 U/mL to be eligible for Segment I. * Platelet count of \>75,000/µL on the day of vaccination with the Janssen Ad26.CoV2.S vaccine. * Contraceptive (birth control) use should be consistent with local regulations regarding the acceptable methods of contraception for those participating in clinical studies. * Before randomization, participants must be either: * Not be of childbearing potential * Of childbearing potential and practicing an acceptable effective method of contraception. Subject must agree to remain on contraception from date of consent until 3 months after the last dose of the Janssen Ad26.CoV2.S vaccine. Use of hormonal contraception should start at least 28 days before the 1st administration of the Janssen Ad26.CoV2.S vaccine. The sponsor-investigator should evaluate the potential for co…