Little is known about the MIS-C risk with different SARS-CoV-2 variants. In Southeast England, MIS-C rates per confirmed SARS-CoV-2 infections in 0-16 years-olds were 56% lower (rate ratio, 0.34; 95%CI, 0.23-0.50) during pre-vaccine Delta, 66% lower (0.44; 0.28-0.69) during post-vaccine Delta and 95% lower (0.05; 0.02-0.10) during the Omicron period.

We postulate that healthcare provider factors manifested by variation in clinical decision-making (including thresholds for admission and discharge, and variation in therapies) are responsible at least in part for variation in rate of admission and length of stay for children with bronchiolitis in England.

The study of geographical variation in healthcare has moved on since J Allison Glover's seminal study in 1938, and its value in highlighting inequity in access, quality and outcomes is well-established. Study of variation in healthcare for children, however, has proven more difficult due to barriers with data and idiosyncrasies in how we measure outcomes for children and families. This paper is a narrative review of unwarranted variations in healthcare for children, and discusses the potential of variation analysis to help researchers and policy makers improve child health services.

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