For a study, researchers sought to calculate series completion for the 2 Meningococcal serogroup B (MenB) vaccines that were currently available: MenB 4-component (MenB-4C, doses at 0 and 1 month) and MenB factor H binding protein (MenB-FHbp, doses at 0 and 6 months). Participants in this retrospective health insurance claim data analysis were 16–23-year-olds who began MenB vaccination (index date) between January 2017 and November 2018 (MarketScan Commercial Claims and Encounters Database) or January 2017 to September 2018 (MarketScan Multi-State Medicaid Database) and had continuous enrollment for ≥6 months before and ≥15 months after index (MarketScan Commercial Claims and Encounters Database). The key result was the completion of the MenB vaccination series in 15 months. Preventive care/well-child visits and vaccine administrative office visits were recognised as potentially missed chances for series completion among non-completers. Independent predictors of series completion were discovered using robust Poisson regression models. Series completion was 56.7% in the Commercial (n=156,080) and 44.7% in the Medicaid (n=57,082) populations, respectively, and was higher among those who started MenB-4C versus MenB-FHbp (61.1% versus 49.8% and 47.8% versus 33.9%, respectively; both P<0.001). 40.2% and 34.7% of non-completers in the Commercial and Medicaid groups had 1 missed opportunity to complete the series. Receiving MenB-4C and being younger were linked to a higher likelihood of series completion. Series completion rates were below average, while those who started MenB-4C had a better success rate. Interventions to promote completion and prevent missed opportunities should be adopted to optimise the effects of MenB immunisation.