AH, VH, SH, PK, SD, and AR were responsible for the original design and preparation of this Correspondence. AS and NP collated and analysed the secondary immunodeficiency cohort measles and clinical data and contributed to the writing of the Correspondence and figures and table preparation. SF was responsible for the measles testing of the COCO cohort, analysis of birth groups, and figure and table preparation. OG was responsible for the measles testing of the VIBRANT cohort, analysis, and contributed to writing of the Correspondence. AS and AR have accessed and verified all underlying data. All authors had full access to the data in the Correspondence and had final responsibility for the decision to submit for publication. We declare no competing interests related to this Correspondence. AH has received unrelated grant funding from Wellcome Trust, Medical Research Council (MRC), British Society for Antimicrobial Chemotherapy, and Medical Research Foundation. AH acts as a clinical consultant for the WHO Global Influenza Programme, Department of Health and Social Care Scientific Advisory Group for Serology Testing, National Institute for Clinical Excellence, and Scotland Medicines consortium; and is a data monitoring committee member for the BALANCE trial (NCT03005145). AR has received unrelated grant funding from UK Research and Innovation (UKRI) and MRC. SD has received unrelated grant funding from MRC, UKRI, National Institute for Health and Care Research, and Wellcome Trust. VH has received unrelated grant funding from MRC and Health Data Research UK, and is supported by the UK Health Security Agency and the UK Department of Health. The authors welcome applications from researchers looking to use the data published herein. Applications should be directed to the corresponding author and will be reviewed by the authorship group and subject to the establishment of data sharing agreements. This work is a compilation from three different studies and four different funding sources where data on measles immunity has been tested as part of the study and then combined to provide the narrative in this Correspondence. The COCO study was funded by the UK Medical Research Council. The VIBRANT and SIREN studies were funded by UK Research & Innovation COVID-19 Rapid Response Initiative. Laboratory validation and verification of the measles ELISAs was supported by funding from the UK Medical Research Council (MX/X502996/1). Relevant Ethics committee approvals were from Camden and Kings Cross Research Ethics Committee (20/HRA/1817) for the COCO study and the Chelsea Research Ethics Committee (21/HRA/5433) for the VIBRANT study.