AimsThe meningococcal B vaccine, which was introduced to the routine vaccine schedule in the UK in September 2015, has been linked with fever post-administration with estimates of fever occurring in over 50% of children who receive the vaccine. The first dose of the vaccine is given at 2 months old. Fever in children under 3 months is a red flag symptom for sepsis according to the National Institute for Health and Care Excellence guidelines and may warrant further investigations including a lumbar puncture.The objective of this study is to review whether the introduction of the meningococcal B vaccine has increased rates of lumbar punctures in children aged one to three months admitted to hospitals in England.MethodsChildren aged 29 to 90 days, who had a lumbar puncture during a hospital admission in England, between financial years 2010/11 and 2019/20 were identified using the Hospital Episodes Statistics (HES) dataset. Rates of lumbar puncture were calculated using population estimates from the Office of National Statistics. ICD-10 codes for meningitis were identified and rates of meningitis as the primary diagnosis, using the first diagnostic code from the HES dataset, were calculated.ResultsAs shown in figures 1 and 2, rates of lumbar puncture have increased over the last decade. The highest rates occurred in the financial year 2016/17 with a rate of 4581 lumbar punctures per 100,000 person-years (4460,4706 95%CI). This was the year following the introduction of the meningococcal vaccine, suggesting that the introduction of the meningococcal B vaccine may be linked to increased lumbar puncture rates. Rates have then reduced in subsequent years. This may be due to increased recognition of vaccines as a cause of fever or greater use of antipyretic medications at the time of vaccination. The median length of admission for infants aged 29 to 90 days was 3 days (2,4 IQR).The cause of the general increase in lumbar puncture rates over the last decade is unclear. One possible cause is improved coding of lumbar punctures rather than a genuine increase in rates.Rates of meningitis have however remained relatively static over this time period as shown in figures 1 and 2. Rates have ranged between 75 and 92 cases per 100,000 person-years in one–to-three-month-old infants in England.Abstract 1283 Figure 1Graph to show the change in rates of lumbar puncture and primary diagnosis of meningitis in 29-to-90-days olds in England from financial years 2010/11 to 2019/20Abstract 1283 Figure 2Rates of lumbar puncture and rates of meningitits as primary diagnosis in 29-to-90-days olds in England from financial years 2010/11 to 2019/20ConclusionOur results suggest that the introduction of the meningococcal B vaccine may be linked to increased rates of lumbar puncture. The increasing rate of lumbar punctures in England, despite static rates of meningitis, suggests we may need to consider alternative approaches to assessing febrile infants, such as the ‘Step-by-Step’ Approach.