A living systematic review is an evidence synthesis that is continuously updated as new relevant evidence becomes available, rather than being published as a static, one-time product. Instead of conducting a systematic review, publishing it, and letting it become outdated as new studies emerge, a living review maintains ongoing evidence surveillance, screens new studies against existing eligibility criteria, and periodically re-analyzes the accumulated evidence to determine whether conclusions have changed.
The concept gained significant momentum during the COVID-19 pandemic, when evidence on treatments, vaccines, and public health interventions was evolving so rapidly that traditional systematic reviews became outdated within weeks of publication. Hundreds of living systematic reviews were published during the pandemic, demonstrating the approach's value for rapidly evolving evidence landscapes. The Cochrane Collaboration has since formalized living review methodology for its Cochrane Database of Systematic Reviews.
How a Living Systematic Review Works
The living systematic review process follows the same initial steps as a traditional systematic review but adds an ongoing cycle of surveillance, screening, and re-analysis.
Phase 1: Initial Review (Same as Traditional)
- Develop and register a protocol on PROSPERO specifying the living review methodology
- Conduct a comprehensive explore search strategy across relevant databases
- Screen, extract data, and assess risk of bias
- Conduct meta-analysis explained or narrative synthesis
- Publish the initial version with prisma 2020 explained reporting
Phase 2: Ongoing Surveillance (Unique to Living Reviews)
- Regular searches. Run updated database searches at defined intervals (monthly, quarterly)
- Screen new records. Apply existing eligibility criteria to newly identified studies
- Assess triggers. Determine whether new included studies warrant re-analysis based on predefined criteria
- Extract and assess. Extract data from new included studies using existing extraction forms and assess risk of bias
- Re-analyze. Update the read about meta-analysis or synthesis with the new data
- Publish update. Release a new version of the review with clear version numbering
Phase 3: Retirement
When predefined retirement criteria are met, the living review reverts to a static systematic review with a final publication date.
When Is a Living Systematic Review Appropriate?
The Cochrane Living Evidence Network recommends living reviews when three conditions are met simultaneously:
- The question is a high priority for clinical practice, public health, or policy decisions
- There is important uncertainty in the current evidence, meaning the existing conclusions could change with new data
- New evidence is being published at a rate that could change the review's conclusions within the planned update interval
If any of these conditions is not met, a traditional systematic review with planned periodic updates is more appropriate and resource-efficient.
Examples of appropriate living review topics:
- Effectiveness of new treatment classes where trials are actively being published
- Safety surveillance for medications with emerging safety signals
- Public health interventions during ongoing outbreaks or pandemics
- Clinical questions where practice guidelines are being actively revised
Examples where living reviews are NOT appropriate:
- Historical questions where the evidence base is stable
- Questions where all relevant trials have been completed and published
- Topics with very low rates of new evidence publication
