In terms of population estimates, this is from the notes section of the weekly NHS vaccinations file, and the rationale for why I've been using the NIMS figures (which of course being live can change each week, not hugely of course).
Population/cohort size (denominator) definitions
Alongside these data, the publication includes estimates of cohort sizes, which can be used as a denominator to calculate approximate vaccination uptake percentages. Two denominators are used:
1. Office for National Statistics (ONS) 2019 mid-year population estimates are provided as the official statistics and the best publicly available population estimates. This publication uses ONS denominators for National, Regional, Integrated Care System (ICS) / Sustainability Transformation Partnership (STP) and Clinical Commissioning Group (CCG) geographies. These estimates are consistent with the UK COVID-19 vaccines deployment plan and therefore provide a reference point on progress. They are the most accurate estimates available at national level, however they are less robust at smaller areas and are subject to a degree of uncertainty as they are 2019 estimates based on the 2011 Census.
2. National Immunisation Management System (NIMS) denominators are also provided for Middle Layer Super Output Area (MSOA), Lower Tier Local Authority (LTLA) and Constituencies. NIMS denominators facilitate management of the vaccination programme at more granular levels and should be used when calculating vaccine coverage for public health purposes. NIMS denominators may provide an overcount if individuals are no longer resident in England, but may also be subject to some undercounting as they currently do not include individuals without an NHS number. Coverage can be viewed as being ‘at least’ the figures presented using the NIMS denominator. The NIMS denominators are based on the resident population and therefore people will be counted in the denominators if they live in England, even if their GP practice is in Wales or Scotland and they receive their vaccination outside of England. Therefore, when looking at lower levels of geography, areas near the borders may appear to have lower vaccine uptake rates than other areas of England.
An interesting exercise is to compare the ONS and NIMS figures at LA level - Oxbridge standout again. I do wonder whether Sir Humphrey was on to something
Census 2021 data is someway off still - as the mop ups continue into May for starters.