COVID vaccine data quality, cleaning, and management

When COVID-19 vaccines were introduced in late 2020 and widely distributed in early 2021, states were responsible for collecting and managing the data. In the best situation, states kept accurate records of each person who received the vaccine, including the age and the county of residence. States reported the cumulative number of those vaccinated in each county, although there were substantial numbers of vaccine recipients (within a given state) whose county of residence was unknown. Some states have very low numbers of vaccine recipients with unknown county, while other states reported upwards of 50% “unknown county of residence.” At the extreme, Texas did not report the county of residence until October 2021, although they did report the state-wide total. There were a number of states that reported a nearly simultaneous jump in the cumulative number of those vaccinated whose county of residence was known and a drop in the number of “unknowns,” likely caused by a retrospective analysis and reallocation of those whose county of residence was unknown. A further problem occurs when the cumulative number of vaccines drops. We describe how we created a database for county-level vaccine data that addresses these data quality issues.