Understanding Long COVID-19

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Last Updated: April 7, 2021

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This Briefing Note was completed by the Evidence Synthesis Unit (Research, Analysis and Evaluation Branch, Ministry of Health) in collaboration with a member of the COVID-19 Evidence Synthesis Network. Please refer to the Methods section for further information.

Purpose

This note summarizes the research evidence associated with “long COVID”, including definitions, risk factors, symptomatology, prognosis, and emerging research findings or trends.

*The full version of the Briefing Note including the Appendix can be accessed in the PDF file at the top of the page*

Key Findings

Commonly, long COVID is characterized as the persistence of any COVID signs and symptoms that continue or develop between four to 12 weeks after acute COVID-19, including both ongoing symptomatic COVID‑19 and post‑COVID‑19 syndrome.

Ten systematic and narrative reviews (including three preprint studies), representing approximately 334 international studies, provided the following details:

Limitations

The limited evidence base currently precludes a precise definition of COVID-19 symptoms and prevalence. In addition, no identified studies provided evidence regarding prognosis for individuals with long COVID. There is a clear need for robust, controlled, prospective cohort studies, including different at-risk populations and settings, incorporating appropriate investigations, collected and recorded in a standardised way.

Analysis for Ontario

Since the time frame for assessing the risk factors and symptoms associated with long COVID has just been seven months, there has been scant time to understand the longer-term implications of COVID-19 infection.

Supporting Evidence

This section below summarizes the emerging research evidence associated with ‘long COVID’, including definitions, risk factors, symptomatology, prognosis, and emerging trends or findings.

Scientific Evidence

  • ‘Long COVID’ Defined: The hashtag ‘#Long COVID’ has been frequently used in social media; however, according to the identified literature, long COVID lacks a commonly accepted case definition. Commonly, long COVID is characterized as the persistence of any COVID signs and symptoms that continue or develop between four to 12 weeks after acute COVID-19, including both ongoing symptomatic COVID‑19 and post‑COVID‑19 syndrome. More formal definitions have also been proposed (see Table 2 in the Appendix).
  • Emerging Research Findings: Ten systematic and narrative review (including three preprint studies), representing approximately 334 international studies, provided the following details (see Table 3 in the Appendix):
    • Risk factors: The identified studies suggest that the following factors may increase the risk for long COVID: a higher acuity of COVID-19 infection or presence of many acute COVID-19 symptoms, older age, female sex, obesity, pre-existing comorbidities, psychiatric disorders, and being a health care worker.
    • Symptomatology: The most common symptoms reported were: fatigue, dyspnea (e.g., shortness of breath), headache, and pain (e.g., chest, joint, muscle); however, persistent symptoms have been described for the cognitive, musculoskeletal, respiratory, gastrointestinal, cardiac, and psychological systems.
  • Limitations: The limited evidence base currently precludes a precise definition of COVID-19 symptoms and prevalence. In addition, no identified studies provided evidence regarding prognosis for individuals with long COVID. There is a clear need for robust, controlled, prospective cohort studies, including different at-risk populations and settings, incorporating appropriate investigations, collected and recorded in a standardized way.

Methods

Individual peer-reviewed articles and review articles were identified through PubMed, and Google Scholar. The search was limited to English sources and therefore may not capture the full extent of initiatives in non-English speaking countries. Full-text results extracted were limited to those available through Open Access or studies made available to the Ministry by our partners.

The COVID-19 Evidence Synthesis Network is comprised of groups specializing in evidence synthesis and knowledge translation. The group has committed to provide their expertise to provide high-quality, relevant, and timely synthesized research evidence about COVID-19 to inform decision makers as the pandemic continues. The following members of the Network provided evidence synthesis products that were used to develop this Evidence Synthesis Briefing Note:

  • Evidence Synthesis Unit, Research Analysis and Evaluation Branch, Ontario Ministry of Health; and
  • COVID-19 Evidence Network to support Decision-making (COVID-END).