Background Long Covid occurs in those infected with SARSCoV2 whose symptoms persist or develop beyond the acute phase. We conducted a systematic review to determine the prevalence of persistent symptoms, functional disability or pathological changes in adults or children at least 12 weeks post-infection. Methods We searched key registers and databases from 1st January 2020 to 2nd November 2021, limited to publications in English and studies with at least 100 participants. Studies where all participants were critically ill were excluded. Long Covid was extracted as prevalence of at least one symptom or pathology, or prevalence of the most common symptom or pathology, at 12 weeks or later. Heterogeneity was quantified in absolute terms and as a proportion of total variation and explored across pre-defined subgroups (PROSPERO ID CRD42020218351). Results 120 studies in 130 publications were included. Length of follow-up varied between 12 weeks - 12 months. Few studies had low risk of bias. All complete and subgroup analyses except one had I2 ≥ 90%, with prevalence of persistent symptoms range of 0% - 93% (pooled estimate (PE) 42.1%, 95% prediction interval (PI): 6.8% to 87.9%). Studies using routine healthcare records tended to report lower prevalence (PE 13.6%, PI: 1.2% to 68%) of persistent symptoms/pathology than self-report (PE 43.9%, PI: 8.2% to 87.2%). However, studies systematically investigating pathology in all participants at follow up tended to report the highest estimates of all three (PE 51.7%, PI: 12.3% to 89.1%). Studies of hospitalised cases had generally higher estimates than community-based studies. Conclusions The way in which Long Covid is defined and measured affects prevalence estimation. Given the widespread nature of SARSCoV2 infection globally, the burden of chronic illness is likely to be substantial even using the most conservative estimates.

Background: Long Covid occurs in those infected with SARSCoV2 whose symptoms persist or develop beyond the acute phase. We conducted a systematic review to determine the prevalence of persistent symptoms, functional disability or pathological changes in adults or children at least 12 weeks post-infection. Methods: We searched MEDLINE (Ovid), Embase (OVID), the Cochrane Covid-19 Study register, WHO ICTRP, medRxiv, Cochrane CENTRAL, MEDLINE (PubMed), ClinicalTrials.gov, and the WHO Global research on coronavirus disease (COVID-19) database from 1st January 2020 to 2nd November 2021, limited to publications in English. We included studies with at least 100 participants. Studies where all participants were critically ill were excluded. Articles were screened independently by two reviewers, with disagreements resolved by a third. Long Covid (primary outcome) was extracted as prevalence of at least one symptom or pathology, or prevalence of the most common symptom or pathology, at 12 weeks or later. Heterogeneity was quantified in absolute terms and as a proportion of total variation and explored across pre-defined subgroups (PROSPERO ID CRD42020218351). Findings: In total 120 studies in 130 publications were included. Length of follow-up varied from 12 weeks to over 12 months. Few studies had low risk of bias. All complete and subgroup analyses except one had I2 ≥ 90%, with prevalence of persistent symptoms ranging between 0% and 93%. Studies using routine healthcare records tended to report lower prevalence of persistent symptoms/pathology than self-report. However, studies systematically investigating pathology in all participants at follow up tended to report the highest estimates of all three. Studies of hospitalised cases had generally higher estimates than community-based studies. Interpretation: The way in which Long Covid is defined and measured affects prevalence estimation. Given the widespread nature of SARSCoV2 infection globally, the burden of chronic illness is likely to be substantial even using the most conservative estimates.