Vaccine Cold Chain Performance Across Seven Provinces and Two Seasons in Nepal: Findings from a Nationwide Temperature Monitoring Study

Abstract

Background: Maintaining vaccines at 2–8 °C from manufacture to administration is a prerequisite for potency, yet cold chain failures remain common in low- and middle-income countries. The World Health Organization (WHO) recommends that every country conduct a temperature monitoring study (TMS) at least once every five years to identify and correct weaknesses in its vaccine supply chain. Nepal’s first national TMS was conducted in 2015–2016 and reported in 2018. The second was conducted seven years later, in 2025. We report its findings across both winter and summer seasons. Methods: Two cross-sectional temperature monitoring studies were conducted across seven supply chain routes, one per province, from the Central Vaccine Store (CVS) in Kathmandu to service delivery points. Study 1 (winter, January to March 2025) covered six routes; Study 2 (summer, April to July 2025) covered all seven. A total of 24 facilities across five supply chain levels were included, selected to represent Mountain, Hill, and Terai districts, rather than a statistically representative sample of all such facilities nationwide. WHO-prequalified data loggers (LogTag UTRID-16, primary; Vac-TL-01, backup) recorded temperatures at 30-min intervals. Two vaccines were tracked: Pentavalent (freeze-sensitive) and oral polio vaccine (OPV, heat-sensitive). Mean kinetic temperature (MKT) and percentage of time in the 2–8 °C range were the primary outcome measures. Results: Total monitoring time was 18,187 h (7787 winter; 10,400 summer). The mean percentage of time the vaccines were within the safe 2–8 °C range was 98.1% (95% CI 96.3–99.6%) of monitored time in winter (Study 1) and 97.4% (95% CI 95.4–99.1%) in summer (Study 2). However, vaccines were below 2 °C for a cumulative 272.5 h (1.5% of total time), concentrated in storage at the cold chain point and service delivery point levels, with one route recording −12.1 °C. Heat excursions above 8 °C totaled 155.0 h (0.9%), concentrated in storage at the central and provincial vaccine stores and in the transit between them. Vaccine vial monitors (VVM) were all at the usable stage, but slightly faded VVM readings for OPV indicated cumulative thermal stress. Conclusions: Nepal’s vaccine cold chain remained within 2–8 °C for more than 97% of monitored time in both seasons, and MKT values stayed within the recommended range; however, route-level data identified persistent sub −2 °C exposures (cumulatively 272.5 h, with one route reaching −12.1 °C). Because mean kinetic temperature is heat-weighted and the study did not include shake testing, the integrity of Pentavalent vaccine on routes with sub-zero excursions cannot be confirmed from these data alone. Recommendations requiring minimal capital investment, differentiated by season and route, include use of temperature-regulated loading areas, ice-pack conditioning training, updated standard operating procedures (SOPs) for transit, refrigerated-vehicle maintenance, replacement of last-mile cold boxes and carriers with freeze-preventive models, and extension of cold chain points.