Understanding reported COVID-19 cases in England following changes to testing, between November 2021 and April 2022

Abstract

Background Over the course of the pandemic, testing policies for SARS-CoV-2 have varied considerably in England, particularly in the five months up to 1 April 2022 when free community testing ended. We described the trends and demographics of COVID-19 cases during this period. Methods COVID-19 cases reported between 15 November 2021 and 30 April 2022 were extracted and aggregated by testing pillar: Pillar 1 for those tested within the NHS, private or public health laboratories, and Pillar 2 for community testing. COVID-19 cases were described by epi-week, and stratified by test type, age, sex, index of multiple deprivation (IMD), region, and population density. Incidence rates were also calculated and stratified by IMD and region. Results Of 10,196,425 COVID-19 cases, 7.3% were reported under Pillar 1 and 92.7% under Pillar 2. From 15 November 2021 to 31 March 2022, most Pillar 2 cases were tested either by polymerase chain reaction (PCR) only or PCR with lateral flow device (LFD) (70.8%) and three in ten cases tested using LFD only. However, between 1 April and 30 April 2022 this rose to nine out of ten cases testing using LFD only. Over the whole period studied and under both pillars, the majority of cases were female (55.2%), resided in the South East (17.0%) and in the age group 30-39 years (18.6%). Trends in IMD and population density varied over the period. When stratifying by IMD the highest case numbers and incidence rates reported under Pillar 1 and NHS were in those in the most deprived quintile. This was also seen for cases reported under Pillar 2 by LFD until 11 January 2022, where a reverse in the trend occurred with the highest cases and rates in the least deprived quintile. This same pattern was observed when describing the cases by population density, with Pillar 2 LFD reported cases being highest in the most densely populated regions until 11 January, from when there was a switch to the highest cases being in the least densely populated regions. Conclusion Differences and trends were observed in reported COVID-19 cases in England, particularly those tested under Pillar 2 following the introduction of testing policy changes. To better understand the impact of these changes over the course of the COVID-19 pandemic, as well as to predict the impact of future testing policies, it would be beneficial to investigate the accessibility of testing amongst different populations. Currently, Pillar 1 COVID-19 cases are likely to be more representative of symptomatic cases requiring testing for a clinical need, as these are less impacted by variations in testing patterns compared to Pillar 2. However, a limitation of that approach is that use of Pillar 1 alone would be biased towards those more likely to be clinically unwell.

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