The last mile of vaccine delivery is not a logistical metaphor. In Senegal's Tambacounda and Kedougou regions, it is a literal dirt road that washes out in the rainy season, leading to a health post staffed by a single nurse who, until recently, kept vaccines in a kerosene-powered refrigerator that worked intermittently and failed silently. Children were immunised with vaccines that had lost efficacy in broken cold chains, or not immunised at all when supply runs could not reach the post reliably.

The Senegal Solar Immunisation Program, implemented between 2021 and 2024 with funding from GAVI, UNICEF, and the Islamic Development Bank, installed solar-powered vaccine refrigeration systems with battery backup at 2,800 health posts across all 14 regions. Each unit includes a GSM-connected temperature logger that transmits real-time data to a national cold chain monitoring dashboard in Dakar, alerting regional health officers to excursions within 15 minutes.

The temperature monitoring data reveals the scale of the previous problem: in the first three months after installation, 34 percent of units recorded at least one temperature excursion that would have compromised vaccine efficacy under the old kerosene system. With solar power and automated alerting, that figure has fallen to 1.2 percent. Coverage for all childhood vaccines in rural districts rose from 61 percent in 2021 to 96 percent by end 2024, closing a gap with urban coverage that had persisted for two decades.

The World Health Organization estimates the coverage improvement will avert approximately 28,000 under-five deaths annually from measles, pneumococcal disease, and rotavirus — the three vaccine-preventable conditions most prevalent in the affected regions.

"The vaccine existed," said Minister of Health Marie Khemesse Ngom Ndiaye. "The electricity did not. That was always the fixable problem."