This November 2025 document is version 5 of the Poliovirus Outbreak Response Assessment (OBRA) Aide Mémoire — the reference guide for the structured, independent assessment conducted to evaluate the adequacy of immunization and surveillance response to an active poliovirus outbreak. Developed jointly by GPEI agencies and revised based on feedback from regional WHO and UNICEF teams, version 5 updates the scope, timing, and emphasis of OBRA assessments.

The OBRA addresses a fundamental challenge: ensuring that vaccination and surveillance response is robust enough — in terms of coverage, quality, geographic scope, and timing — to interrupt transmission. While routine monitoring data provide performance signals, an independent field assessment provides unmediated ground-truth evaluation that programmatic data systems may not capture.

The document states the OBRA's purpose: to assess whether vaccination and surveillance response is robust enough to detect and stop poliovirus transmission, and to identify what is needed to address gaps. OBRAs are designed to be timely (conducted 6–8 weeks after the first response round), effective (producing actionable recommendations), practical (feasible in field environments where outbreaks occur), and independent (conducted by teams with no line accountability to the national program being assessed).

The three core OBRA objectives are: assessing and strengthening immunization coverage and population immunity (primary priority when transmission is ongoing); assessing and strengthening surveillance sensitivity to levels needed to detect virus transmission and interruption; and assessing early progress towards interrupting transmission.

Version 5 revisions include updated timing guidance recognizing how each successive OBRA's focus, scope, and emphasis evolves as an outbreak ages, with clearer guidance on adjusting emphasis based on outbreak phase and time elapsed since the last isolate.

Who should read this: OBRA team members and coordinators, WHO regional and country office outbreak response staff, UNICEF emergency response coordinators, GPEI partner organization technical staff, national program managers hosting OBRA visits, IMB members.

Document value: Operational guide for independent outbreak response assessments, providing the framework that ensures polio responses are evaluated against objective standards and that gaps are identified before they allow transmission to continue unchecked.