Towards Low-Carbon and Climate-Resilient Immunization Supply Chains Through Reduced Waste, Environmental Impact and Carbon Emissions

3.1. Overview of the Evidence Base

The evidence identified for this review shows that immunization supply chains generate environmental impacts across multiple stages of the vaccine lifecycle. The strongest available evidence relates to cold-chain energy use, international supply-related emissions, solar-powered refrigeration, healthcare waste management and selected operational case studies. Evidence is less developed for complete life-cycle emissions of routine immunization programmes, embedded emissions in ancillary supplies, end-of-life management of cold-chain equipment, and comparative carbon impacts of different last-mile delivery models.

The available studies and reports do not use a uniform carbon-accounting boundary. Some sources focus on international procurement and freight, while others examine in-country storage, vaccine transport, waste treatment, cold-chain equipment, specific vaccine platforms or individual country case studies. Estimates are therefore not directly comparable across settings. The evidence supports identification of recurrent environmental hotspots and mitigation opportunities, but it does not yet support a single robust global estimate of emissions from all routine immunization supply-chain activities.

Across the available literature, four domains consistently emerge as the main environmental concern areas: energy use for vaccine refrigeration; transport and logistics; production, packaging and use of vaccines and ancillary supplies; and immunization-related healthcare waste management. Cross-cutting issues include digital stock visibility, temperature monitoring, cold-chain equipment lifecycle management, healthcare worker training, financing, and integration of environmental indicators into immunization supply-chain performance systems [5,6,7,8,9,10,11,12,13,14,15].

3.2. Carbon-Emission Hotspots in Immunization Supply Chains

The most comprehensive institutional evidence comes from UNICEF’s international supply-chain emissions baseline, which estimated Scope 3 emissions from UNICEF Supply Division-controlled international supply at 3.9 million tonnes of carbon dioxide equivalent in 2019 [9]. Vaccines, cold-chain equipment, nutrition products and international freight together accounted for 80–90% of UNICEF’s international supply-related Scope 3 emissions [9]. Although this estimate reflects UNICEF’s international supply operations rather than the full global immunization supply chain, it identifies procurement, cold-chain equipment and freight as major emission-sensitive components of vaccine delivery systems.

Cold-chain energy use is a recurring emissions hotspot because vaccines require continuous temperature-controlled storage. Most routine vaccines are stored between 2 °C and 8 °C, while some vaccine platforms require frozen or ultra-cold storage. Energy demand arises from national cold rooms, subnational stores, health-facility refrigerators, freezers, passive cooling systems, temperature monitoring devices and backup power arrangements. In low- and middle-income countries, the emissions impact of refrigeration is shaped by grid reliability, electricity source, dependence on diesel generators, equipment age, insulation quality, preventive maintenance and load-management practices [5,6,9,13].

Transport-related emissions occur across international and domestic supply chains. International freight contributes to emissions through air, sea and road transport from manufacturers and global procurement hubs to countries. Domestic transport contributes through distribution from national stores to regional, district and health-facility levels, and through outreach or last-mile delivery. Emission intensity is influenced by shipment mode, distance, load factor, route design, vehicle type, cold-chain requirements, emergency deliveries and reverse logistics for waste or empty safety boxes [9,13].

A third emissions domain is the production, packaging and use of vaccines and ancillary supplies. Immunization services depend on glass vials, rubber stoppers, plastic syringes, needles, safety boxes, labels, secondary packaging, cold boxes, ice packs, coolant packs and other materials. These products carry embedded emissions from raw materials, manufacturing, sterilization, packaging and transport. The emissions profile varies by vaccine presentation, number of doses per vial, cold-chain requirement, wastage rate, packaging design and ancillary product type. Published evidence remains limited on the comparative life-cycle impact of different vaccine presentations and delivery devices in routine immunization settings [9,15].

The fourth major domain is healthcare waste. Immunization generates infectious and non-infectious waste, including used syringes and needles, safety boxes, empty or partially used vials, diluent containers, packaging, personal protective equipment during campaigns, and general session waste. The environmental impact depends not only on waste volume but also on segregation, storage, transport, treatment and final disposal. Open burning and low-temperature incineration are especially concerning because they may emit particulate matter, carbon monoxide, dioxins, furans and other pollutants while also contributing to greenhouse-gas emissions [10,11,16].

3.3. Cold-Chain Energy Use and Equipment Lifecycle

Cold-chain equipment is central to vaccine potency but also represents a major environmental and operational concern. Older refrigerators and freezers may consume more electricity, perform poorly under unstable voltage conditions, and require frequent repair. In settings with unreliable grid electricity, diesel generators, gas-powered refrigerators, kerosene units or battery-dependent systems may add cost, emissions and maintenance burden. The environmental impact of cold-chain equipment therefore extends beyond electricity use to include refrigerants, insulation foams, compressor oils, batteries, electronic temperature monitoring devices, spare parts, solar-system components and end-of-life disposal [11,12].

Solar direct-drive refrigeration and solarized cold rooms are among the most mature low-carbon interventions for vaccine storage. The Tunisia Project Optimize pilot demonstrated that integrated vaccine and medicine storage, optimized delivery circuits, solar photovoltaic systems and electric vehicles could reduce emissions while maintaining cold-chain performance. Reported reductions reached 29% for transport emissions and 68% for storage emissions at regional level, and 18% for transport emissions and 59% for storage emissions at district level, compared with baseline [13]. The intervention combined energy substitution, system redesign and route planning rather than treating refrigeration as an isolated technology issue.

Lebanon provides a more recent example of solarized vaccine storage at scale. During a period of severe electricity instability, more than 1,000 solar direct-drive vaccine refrigerators were deployed across more than 800 health facilities. The intervention improved resilience of vaccine storage by reducing dependence on unstable grid electricity and generators and was associated with improved cold-chain reliability and reduced vaccine wastage risk [14].

Large-scale procurement platforms have also accelerated the shift towards more efficient cold-chain equipment. Gavi’s Cold Chain Equipment Optimisation Platform has supported the installation of more than 65,000 cold-chain equipment units across 47 Gavi-supported countries, with solar-powered refrigeration technologies accounting for approximately 60% of installed units [17]. This indicates that solar vaccine refrigeration has moved beyond small pilots and is now a widely deployed cold-chain option in Gavi-supported immunization systems. The environmental benefit of these investments depends on long-term maintenance, technician availability, spare-parts supply, warranty performance, equipment uptime and safe end-of-life disposal [12,17].

Cold-chain equipment decommissioning remains an under-addressed lifecycle issue. Decommissioned refrigerators, freezers, cold rooms, voltage stabilizers, batteries, remote temperature monitoring devices and solar-system components can create environmental and occupational risks if dismantled informally or discarded without refrigerant recovery, oil handling, component segregation and controlled recycling. Risks are particularly relevant for equipment containing ozone-depleting or high-global-warming-potential refrigerants, compressor oils, insulation foams, lead-acid or lithium batteries, circuit boards and metal components [12]. Available evidence indicates that immunization programmes often focus strongly on procurement and installation, but less consistently on decommissioning plans, inventory updating, reverse logistics and environmentally sound disposal [11,12].

3.4. Transport and Logistics

Transport is a recurring source of emissions in immunization supply chains because vaccines and ancillary supplies move through multiple tiers before reaching vaccination sites. International transport may involve air freight, sea freight, refrigerated containers and road transport. In-country transport may involve trucks, refrigerated vans, motorcycles, boats, bicycles, drones or outreach carriers, depending on geography and service-delivery model. The emissions contribution of transport depends on distance, transport mode, fuel type, cold-chain intensity, route efficiency, shipment consolidation, emergency deliveries and return logistics [9,13].

Evidence from Tunisia suggests that logistics optimization can reduce emissions while improving service efficiency. The Project Optimize intervention integrated vaccine and medicine distribution and introduced planned delivery circuits rather than relying on fragmented or ad hoc movements [13]. This finding indicates that transport decarbonization is not limited to replacing diesel vehicles with electric vehicles. Better route design, shipment consolidation, scheduled deliveries, load optimization and integration with compatible health commodities can reduce unnecessary trips and improve the environmental efficiency of vaccine delivery [13].

Digital systems can support transport and logistics efficiency by improving stock visibility and reducing avoidable emergency redistribution. India’s Electronic Vaccine Intelligence Network digitized vaccine stock and cold-chain temperature monitoring through smartphone and cloud-based systems, supporting real-time visibility of vaccine stocks, flows and storage conditions across cold-chain points [7]. Although eVIN was not designed primarily as a carbon-reduction intervention, its ability to reduce stock uncertainty, improve accountability and support timely corrective action has indirect relevance for environmental sustainability. Better information systems can reduce overstocking, emergency transport, vaccine wastage and avoidable supervisory visits when linked to structured supply-chain decision-making [7].

Despite these opportunities, transport-related evidence remains incomplete. Few published studies compare emissions from different last-mile delivery models, such as motorcycles, refrigerated vans, boats, drones, community-based delivery models or integrated primary healthcare commodity distribution. Evidence is also limited on the net carbon effect of electric vehicles in immunization supply chains, because benefits depend on electricity source, battery lifecycle, vehicle utilization, charging infrastructure, maintenance capacity and replacement planning [9,13,17].

3.5. Vaccine Products, Packaging and Ancillary Supplies

Vaccination services depend on a wide range of single-use and multi-component products. These include vaccines, vials, stoppers, labels, secondary packaging, diluents, syringes, needles, safety boxes, cold boxes, ice packs and session-level supplies. Each product has environmental implications through raw material extraction, production, sterilization, packaging, transport, use and disposal. However, published evidence on embedded emissions in vaccine and ancillary product manufacturing remains limited compared with evidence on cold-chain and transport systems [9,15].

Vaccine presentation has important environmental implications. Multi-dose vials may reduce packaging material per dose but can increase open-vial wastage if session size is small or if open-vial policies are not implemented correctly. Single-dose presentations may reduce wastage in some settings but increase packaging, glass and transport volume per administered dose. Prefilled devices, compact prefilled auto-disable devices and needle-free or oral products may reduce some operational barriers but may also introduce different material and disposal requirements. The environmental balance therefore depends on coverage targets, session size, wastage rate, safety profile, cold-chain volume, transport distance and disposal method [9,15].

Thermostable and controlled-temperature-chain approaches offer a potential pathway to reduce cold-chain dependence for selected vaccines. Modelling of a novel thermostable oral COVID-19 vaccine suggests that avoiding cold-chain requirements, needles and some associated consumables could reduce emissions compared with conventional injectable products [15]. However, this evidence is vaccine- and product-specific. It cannot be generalized to all vaccines, and regulatory approval, programmatic suitability, immunogenicity, cost, acceptability and delivery strategy remain central considerations. Controlled-temperature-chain approaches are best understood as targeted tools for specific vaccines and contexts rather than replacements for routine cold-chain systems [15].

3.6. Immunization-Related Healthcare Waste

Immunization-related waste includes sharps waste, infectious waste, non-infectious packaging waste, expired or damaged vaccine vials, diluent containers, cold-chain consumables and waste generated during campaigns. Waste risks are especially high when segregation is weak, safety boxes are overfilled, sharps are handled manually, waste is stored near communities, or final treatment relies on open burning or low-temperature incineration. Poorly managed immunization waste creates occupational risks for health workers and waste handlers, environmental contamination risks for communities, and air-pollution risks from unsafe burning [10,11,16].

The COVID-19 response demonstrated the scale of healthcare waste pressures during emergency vaccination and pandemic response operations. WHO estimated that procurement through the UN emergency system alone generated tens of thousands of tonnes of additional COVID-19-related healthcare waste, while global vaccination activities generated additional waste from syringes, needles and safety boxes [10]. This evidence is relevant to immunization systems because large-scale campaigns can rapidly increase waste volumes in settings where waste segregation, storage, transport and treatment capacity are already limited.

Facility-level evidence from Zambia illustrates the operational gaps that can undermine safe healthcare waste management. In a mixed-methods study across government health facilities, only 37.3% of health workers reported receiving healthcare waste-management training, 56.9% of facilities used infectious-waste bags correctly, 43% had a functional incinerator, and 31.3% of respondents reported a previous needle-stick injury [16]. Although the study covered healthcare waste broadly rather than immunization waste alone, its findings are directly relevant to vaccination services because immunization generates sharps and infectious waste requiring segregation, containment and safe final treatment.

Cold-chain waste mapping expands the definition of immunization waste beyond vaccination-session waste. Cold-chain waste streams include obsolete refrigerators, freezers, cold boxes, coolant packs, packaging, voltage stabilizers, electronic temperature monitoring devices, batteries, solar panels and related accessories [11]. These waste streams are often handled outside conventional healthcare waste-management systems and may fall between immunization, biomedical engineering, environment, energy and procurement responsibilities. This creates policy and accountability gaps. As immunization programmes modernize cold-chain systems, the volume and diversity of non-clinical immunization-related waste is likely to increase, making lifecycle planning essential [11,12].

3.7. Mitigation Interventions and Implementation Evidence

The reviewed evidence suggests that environmental improvements in immunization supply chains are most feasible when they also strengthen programme performance. Solar refrigeration can reduce dependence on fossil fuels while improving vaccine storage reliability. Route optimization can reduce fuel use while improving timely vaccine availability. Digital stock systems can reduce emergency redistribution while improving stock accountability. Better waste segregation can reduce environmental contamination while protecting health workers from sharps injury. These co-benefits make sustainability interventions more acceptable to immunization programmes because they support core objectives of vaccine potency, availability, equity and safety [7,10,13,14,17].

The strongest operational evidence comes from interventions that combine technology with system redesign. In Tunisia, solar power, electric vehicles, integrated storage and optimized delivery routes were implemented as a package [13]. In Lebanon, solar direct-drive refrigerators addressed both energy instability and cold-chain reliability [14]. In India, eVIN addressed visibility of vaccine stocks and temperature monitoring across cold-chain points [7]. In Gavi-supported countries, the Cold Chain Equipment Optimisation Platform has shifted procurement towards higher-performing and more climate-friendly cold-chain equipment, including solar-powered units [17]. These examples indicate that low-carbon immunization supply chains require coordinated planning across procurement, energy, maintenance, logistics, data systems and waste management.

Implementation barriers remain substantial. Solar direct-drive refrigerators require correct site selection, installation quality, preventive maintenance and technician capacity. Electric vehicles require charging infrastructure, spare parts, financing and consideration of grid emissions. Remote temperature monitoring devices generate electronic waste and require connectivity, data use and maintenance systems. Non-burn waste-treatment technologies require segregation at source, reliable electricity, trained operators and final disposal systems for treated residues. Thermostable and controlled-temperature-chain innovations require vaccine-specific regulatory approval and programme guidance. These constraints show that sustainability interventions must be planned as part of the immunization system rather than introduced as isolated technologies [11,12,15,17].

3.8. Evidence Gaps

Several evidence gaps limit the ability to define a complete pathway towards low-carbon and climate-resilient immunization supply chains. First, few complete life-cycle assessments of routine immunization systems include vaccine production, international procurement, in-country distribution, service delivery, cold-chain energy use, waste treatment and cold-chain equipment decommissioning. Second, available studies use different emission boundaries and functional units, making comparison difficult across countries, vaccine products and delivery models. Third, evidence from low-income, fragile and remote settings remains limited, although these contexts may face the greatest combined burden of unreliable energy, long transport routes and weak waste-treatment systems [9,11,12,15].

Fourth, the environmental impact of ancillary supplies remains under-quantified. Syringes, safety boxes, vials, packaging, coolant packs and temperature monitoring devices are central to immunization delivery, but their embedded carbon and end-of-life impacts are rarely measured in routine programme assessments. Fifth, end-of-life management for cold-chain equipment remains a major blind spot. Decommissioning, refrigerant recovery, battery disposal, spare-part reuse, reverse logistics and recycling pathways are rarely included in immunization planning and financing documents [11,12].

Finally, there is limited evidence on how to integrate environmental indicators into existing immunization supply-chain performance systems. Current monitoring frameworks focus mainly on vaccine availability, storage temperature, stock management, wastage, equipment functionality and distribution performance. These indicators remain essential, but they do not fully capture energy efficiency, greenhouse-gas emissions, waste segregation, treatment quality, equipment lifecycle management or sustainability of procurement choices. Future life-cycle assessments should use standardized functional units, such as carbon dioxide equivalent per administered dose and carbon dioxide equivalent per fully immunized child, to improve comparability across studies and settings. Practical indicators could be incorporated into Effective Vaccine Management assessments, national immunization strategies, cold-chain rehabilitation plans, healthcare waste-management plans and donor investment cases [5,6,9,11,12,15].