Objectives To assess the potential use of a protein-based meningococcal group B (MenB) vaccine (Bexsero®) in addition to antibiotic chemoprophylaxis for preventing secondary cases. Methods Published studies on the risk of secondary meningococcal infections were used to estimate the numbers needed to vaccinate (NNV) with Bexsero® to prevent a secondary case in household and educational settings. Results Most secondary cases occur within a few days of diagnosis in the index case. Unlike conjugate vaccines, early protection offered after a single dose of Bexsero® is likely to be low, particularly in young children, who are at higher risk of secondary infection. NNV was dependent on predicted meningococcal strain coverage, estimated onset of protection after one Bexsero® dose and estimated vaccine efficacy. Even in the most favourable scenario where we assume the vaccine is administered within 4 days of the index case and prevents 90% of cases occurring after 14 days, the NNV for household contacts was >1000. NNV in educational settings was much higher. Conclusions The estimated NNV should be taken into account when deciding policy to recommend Bexsero® for close contacts of single cases in household or educational settings. Bexsero® may have a protective role in clusters and outbreaks.