Seroprevalence of measles antibodies in children with cancer: results of a 2024 UK service evaluation.

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.