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Clinical and epidemiological data were collected from 187 clinically diagnosed measles patients in Haj Yousif area, suburban Khartoum. Laboratory tests confirmed the diagnosis in 141 (75%) of the cases, but demonstrated that in 46 (25%) patients the clinical symptoms were not caused by an acute measles virus (MV) infection. According to their vaccination card, 59% of the laboratory-confirmed measles cases had been vaccinated for measles. Compared with non-measles rash disease cases, confirmed measles cases more often had severe illness (P < 0.0001), were dehydrated (P=0.01) at presentation and less likely to recover without complications [OR 0.19 (95% CI 0.09, 0.39)]. There was no difference in death rate (P=0.20). Underweight [weight-for-age Z score (WAZ)

Competing Interests: AB has served on a clinical advisory board for Beckman Coulter and was partly supported by an Antibacterial Resistance Leadership Group Early Faculty Seedling Award from the US National Institute of Allergy and Infectious Diseases (UM1AI104681). NF is the President of the non-profit Sustainable Development Response Organization. ES has received funding from a US Centers for Disease Control and Prevention contract (75D30123P18282) and is a member of the Global Health Committee of the Pediatric Infectious Diseases Society and a member of the Advisory Board of the Sudanese American Medical Association. All other authors declare no competing interests. ZOEB used Grammarly and OpenAI's ChatGPT to improve language and readability of this Comment; the authors reviewed and edited the content as needed and take full responsibility for the manuscript's content.

We conducted a prospective birth cohort study in rural Sudan to assess measles virus (MV)-specific antibody levels at different time points in infancy. Dried blood spots were collected on filter paper at birth (cord blood) and at ages 6, 12 and 24 months (heel-prick). Maternally derived MV-specific antibody levels were high in cord blood samples, but at the age of 6 months had dropped below cut-off values in half of the infants. By extrapolation it was concluded that the current Expanded Programme of Immunization (EPI) target age for measles vaccination of 9 months was an appropriate choice for this area. At the age of 24 months acquired MV-specific antibodies were detected in 65-85% of the cohort, which corresponded well with the 79% of infants reported to be vaccinated by this age. This study demonstrates the usefulness of filter paper blood samples for seroepidemiological studies in developing countries.