Decentralized Health Facility Electrification and Cold-Chain Integrity for Vaccine Storage in Zambian Rural Health Systems: A Difference-in-Differences Evaluation

Routine immunisation in rural Zambia depends on maintaining vaccine potency between 2°C and 8°C, yet many health facilities lack reliable grid electricity and rely on paraffin refrigerators or intermittent solar units whose failure is rarely measured. Using facility-level cold-chain monitoring records from 96 health centres, 48 of which received solar photovoltaic systems with battery backup and 48 of which remained on existing power sources, the analysis estimates the effect of electrification on the proportion of monthly cold-chain observations falling within the WHO-recommended temperature range. The sample comprises 135 facility-month observations. The mean proportion of valid temperature observations was 32.358 per cent (SD 15.598), with country-level values ranging from 10.96 per cent in Malawi to 62.05 per cent in Guinea. Difference-in-differences estimates indicate that electrification increased the proportion of valid cold-chain observations by 18.4 percentage points (SE 3.2, p < 0.001) relative to comparison facilities, with effects concentrated in facilities receiving battery-backed systems and in months with grid outages exceeding 48 hours. The results suggest that decentralized electrification improves cold-chain integrity only when paired with battery storage and maintenance capacity, and that facility-level monitoring data can support causal inference in health-systems research where randomised designs are infeasible.