Seroprotection after Measles Vaccination in Children with Sickle Cell Anemia Receiving Hydroxyurea

Children with sickle cell anemia (SCA) may have decreased antibody responses after some routine vaccines, but it is not known if this affects the response to measles vaccination. It is critical to determine if children with SCA develop adequate seroprotection after measles vaccination considering the rise in measles infections in the United States and persistent transmission globally, particularly in regions with high SCA prevalence. It is also unknown if concurrent hydroxyurea treatment affects the measles antibody response to vaccination. We conducted a retrospective cohort study of children with SCA enrolled on the TREAT trial (NCT02286154) to determine anti-measles seroprotection (IgG ≥ 200 IU/L via ELISA) after first (MV1) and second (MV2) measles vaccine. Seroprotection was reached by 33 of 35 children (94%) after MV1 and by 46 of 50 (92%) after MV2. Each additional year of age at MV2 was associated with decreased odds of seroprotection (odds ratio (OR) 0.25, p=0.02). Hydroxyurea treatment at the time of vaccination did not reduce seroprotection; rather, earlier hydroxyurea initiation was associated with increased seroprotection (OR 4.4, p=0.02). The majority of children with SCA are adequately protected following measles vaccination, similar to the general population, and seroprotection is increased with timely vaccination and early hydroxyurea treatment.