Abstract

Objective To assess measles seroprevalence and testing practices in children with cancer in the UK. Design Multicentre evaluation of measles serology data for children on active treatment for cancer between January and March (Q1) 2024. Setting Eleven UK paediatric oncology centres (eight principal treatment centres and three shared care units). Patients Children aged <18 years on active cancer treatment with measles serology data at diagnosis and/or following revised UK Health Security Agency guidance in Q1 2024. Results A total of 695 eligible patients were included with a median age of 5.2 years (IQR 3.3–10.8 years). Baseline measles serology was tested in 545 patients with 89.0% positive for IgG antibodies. Cross-sectional testing of patients in Q1 2024 was undertaken in 289 patients with 78.5% measles seropositivity. Of the 121 patients tested at both time points who were measles seropositive at diagnosis, 23 (19.0%) were seronegative at retest. Most patients who lost pre-existing humoral immunity had an underlying diagnosis of leukaemia (n=16) followed by non-solid central nervous system (CNS) tumour (n=3), CNS tumour (n=2), lymphoma (n=1) and other (n=1). Although the odds of losing immunity were higher in haematological malignancy groups, this was not statistically significant (OR=1.44, 95% CI 0.52 to 3.99). Conclusions Children with cancer can lose pre-existing humoral immunity to measles during treatment. Variability in testing practices and rising measles cases nationally requires a standardised approach. Retesting measles serostatus during national outbreaks is important to identify susceptible patients who may require postexposure intravenous immunoglobulin.