Inclusion Criteria:  Willing to receive routine COVID-19 vaccination with Pfizer, Moderna or AstraZeneca vaccine. Age: ≥12 years or < 12 years once vaccine is recommended for routine use in the respective age group Either Down syndrome (DS) or household contacts without DS of participant with DS.  Exclusion Criteria:  Down syndrome cohort:  History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (e.g. anaphylaxis) to any component of the study intervention(s). Organ transplant recipients Active malignancy or completion of treatment for malignancy in previous 3 months Infection with Human Immunodeficiency Virus (HIV) Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection.  Healthy control cohort:  - As in Down Syndrome cohort  Plus:  Active medical care for inherited or acquired immune deficiency Any severe comorbidity for which regular medical care is needed (e.g. heart failure, COPD, diabetes)