Measles immunity status in Iranian infants and children and outbreak concerns: Time for reconsidering the vaccination schedule?

Introduction: Measles vaccination has greatly reduced the disease burden worldwide, but challenges remain due to variations in vaccine effectiveness across age groups. This study aimed to assess the serological profile of measles antibodies across different age groups, evaluate the impact of maternal immunity on antibody levels in infants under 12 months, and assess measles immunity in vaccinated individuals. Material and methods: This cross-sectional study was conducted from June 2022 to January 2023 at the Children's Medical Center, a referral hospital in Iran. Serum samples were tested for measles-specific IgG and IgM antibodies using a commercial enzyme-linked immunosorbent assay (ELSA). An avidity assay was performed to assess measles virus-specific IgG antibodies on the samples that were positive and borderline for the measles IgG ELISA. Results: The study included 969 participants across various age groups. Among them, 23% (221 out of 953) tested positive for measles IgM ELISA, and 52% (504 out of 969) for measles IgG ELISA. Regarding the avidity assay for measles virus-specific IgG, the majority (418 out of 573, 73%) showed high-avidity antibodies. Measles-specific IgG levels varied significantly across different age groups, with infants below 6 months old showing a mean IgG level of 477 mIU/mL, declining to 230 mIU/mL between 6 and 12 months, and increasing significantly to 683 mIU/mL in the 12 to 18 month age group, reaching a peak at 938 mIU/mL among children aged 18–72 months. Conclusion: The increasing IgM positivity among young Iranians suggests a rising risk of measles outbreaks, possibly due to vaccination gaps. Inadequate antibody levels in infants raise concerns about vaccination effectiveness. Considering declining maternal antibodies, vaccinating infants at 6–9 months could be beneficial. Boosters for adolescents and women may further mitigate outbreak risks.