1.) Which single design limitation most threatens valid estimates of sensitivity and representativeness? How would you address it within six weeks?
The most significant design limitation that threatens valid estimates of both sensitivity and representativeness in the AEFI surveillance system is the exclusion of private health facilities and some general hospitals from the reporting network. Although surveillance system deploys in Routine Immunization (RI) place, AEFI can be happened anytime after vaccination and omitting some facilities leads to systematic under-reporting and biased estimates. This results in missed AEFI cases, especially from underserved or rural areas, ultimately compromising the system’s ability to detect all true cases (sensitivity) and to reflect the true distribution of AEFI occurrences in the population (representativeness).
To address this limitation within six weeks, the surveillance team could rapidly expand the inclusion of private and all public healthcare facilities into the AEFI reporting network. Short virtual or on-site training sessions could be organized for these facilities to orient staff on AEFI case definitions, data tools, and reporting timelines. A simplified one-page weekly reporting form or a mobile entry system through DHIS2 could be introduced to make reporting easier. In addition, surveillance officers should conduct active follow-up to ensure that each facility submits at least one report within the first month.
By implementing these targeted actions within a six-week period, the surveillance system would achieve broader coverage, reduce under-reporting, and significantly improve both sensitivity and representativeness, leading to more reliable and valid estimates of AEFI occurrence.
2.) Using the CDC surveillance attributes, propose one low-cost intervention to increase sensitivity. State the expected trade-offs, and list 2–3 indicators to detect impact from the intervention.
A low-cost intervention to increase the sensitivity of the AEFI surveillance system, using the CDC surveillance attributes, would be to implement a monthly SMS reminder and feedback system for frontline health workers. This system would send simple text prompts reminding vaccinators to report any observed AEFI cases, including “zero reports” when no cases occur. In return, the system would provide short feedback messages acknowledging receipt of reports and sharing quick data summaries or recognition for timely submissions.
This intervention directly targets the sensitivity attribute by increasing case detection and reporting completeness through frequent engagement and accountability. It reinforces awareness of AEFI case definitions and ensures that even minor or delayed cases are not overlooked due to forgetfulness or competing work priorities.
The expected trade-offs include a potential increase in false-positive or minor AEFI reports, as more health workers may report mild or unrelated events. This may temporarily increase data volume and workload for data validators at the LGA or state level. However, these trade-offs are acceptable because higher sensitivity strengthens early warning capacity and public health responsiveness.
To measure the impact of the intervention, the following indicators could be tracked:
1. Percentage increase in reported AEFI cases per month after implementation (compared with baseline).
2. Proportion of health facilities submitting any AEFI report (including zero reports) each month.
3. Timeliness of AEFI report submission with proportion of reports received within the expected reporting timeframe.
Overall, this low-cost, communication-based strategy would enhance the system’s sensitivity by improving active participation, reducing under-reporting, and fostering a culture of consistent AEFI surveillance among health workers.
3.) For a newly introduced vaccine, should the AEFI case definition be temporarily broadened to maximize early signal detection?
– If yes, what trigger would you use to revert to the prior definition?
– If no, why should this change not be implemented?
Yes. For a newly introduced vaccine, it is appropriate to temporarily broaden the AEFI case definition to maximize early signal detection. During the initial rollout, there is limited real-world data on the vaccine’s safety profile, so widening the case definition increases the sensitivity of the surveillance system, helping to capture even rare or unexpected adverse events that might otherwise be missed. This proactive approach ensures that potential safety concerns are identified and investigated early, building public trust and allowing timely corrective actions if needed.
However, a broadened definition should be time-limited to prevent unnecessary over-reporting and data burden. The system should revert to the standard, more specific definition once certain triggers are met.By applying this temporary, sensitive approach early and returning to the routine definition once sufficient safety data are available, the surveillance system balances vigilance with efficiency, ensuring both early signal detection and long-term sustainability.