Exploring duplication in reviews of Long COVID: 2020-2023

Background The unnecessary duplication of reviews is a recognised problem in the field of evidence synthesis. This paper reports findings from a study exploring potential duplication of effort in reviews on the frequency and/or risk of Long COVID that were published during the first three years of the COVID-19 pandemic. Methods We extracted and summarised the aims and key characteristics of 112 reviews identified from five published evidence summaries commissioned by the National Institute for Health and Care Research (NIHR) for the Department of Health and Social Care (DHSC), England, which covered the period from January 2020 to January 2023. Results There was significant similarity in the aims and characteristics of the 112 reviews. We identified 43 reviews reporting on any persistent symptoms/effects and 69 that focused on specific symptoms/effects; overlap in the conditions studied was common. The majority of reviews focused on individuals of any age (n=62); where restrictions were applied (n=50), all but six reviews focused on adults. Most reviews focused on both hospitalised and non-hospitalised patients (n=97) and authors searched the same time periods. Half of authors reported publishing a protocol prospectively (n=58) and only a minority received specific review funding (n=39). Conclusions Our findings raise concerns about unnecessary duplication of effort and the extent to which all reviews we assessed will have added substantially to the Long COVID evidence base. Researchers should seek to minimise research redundancy and only conduct new reviews when a genuine knowledge gap exists.