Mali is a large country with diverse landscapes, ranging from northern deserts to southern savannas and forests. Spanning 1,240,192 square kilometers, it ranks as the eighth-largest country on the continent. Livestock herding plays a vital role in the economy, with cattle, sheep, goats, and camels being the primary livestock raised. Livestock contributes substantially to household incomes for at least 80% of the rural population, especially women, and accounts for more than 40% of the Gross Domestic Product (GDP) and three quarters of Mali’s exports (1).

According to the livestock estimations provided by the National Directorate of Animal Production and Industries (DNPIA), on 31^st December 2022, 43,913,180 sheep and goats were reared in Mali (2). Unfortunately, productivity in the small ruminants (SRs) sector remains low for several reasons, including high disease burden, high lamb/kid mortality, low growth rates, poor nutritional status and absence of long-term breeding programs, resulting in infertility and long lambing and kidding intervals. Added to that, the inadequate institutional capacity strengthening among actors, plus poor links between producers and markets, make the performance of the SR value chain sub-optimal (3, 4).

One of the most devastating diseases affecting SRs is Peste des Petits Ruminants (PPR). This highly contagious viral disease is caused by a morbillivirus closely related to the rinderpest virus. It primarily affects goats and sheep, as well as wild small ruminants and camelids. PPR was first reported in Côte d’Ivoire in 1942 (5). According to a 2013 serological survey conducted across the administrative regions of Mali (excluding Kidal), the overall individual seroprevalence of PPR was 42.6%. However, prevalence rates varied significantly between regions, ranging from 5.5% in Gao to 55.6% in Koulikoro (6).

The global community is increasingly aware of the high economic burden and devastating consequences of PPR. Although there is no cure, the disease can be effectively prevented through vaccination. Effective live attenuated PPR virus vaccines are widely available. The two most commonly used strains, Nigeria/75/1 and Sungri/96, have demonstrated, in experimental settings, robust protection against all known PPRV lineages (7). The Nigeria/75/1 vaccine has also been proven to provide such complete cross-lineage protection in field use in a large number of countries (8).

Hence, in 2015 the PPR Global Eradication Program (PPR-GEP) was launched under the lead of the World Organization for Animal Health (WOAH) and the Food and Agriculture Organization of the United Nations (FAO) PPR secretariat. The objective of the PPR-GEP is to eradicate PPR by 2030, reinforce veterinary services and reduce the impacts of other major infectious diseases of SRs. This will then contribute to fighting rural poverty, ensuring food security and nutrition and strengthening resilience, national economies and achieving Sustainable Development Goals (SDGs). The PPR-GEP recommends mass vaccination for 2–3 rounds to achieve at least 80% coverage of the sheep and goat population above the age of 3 months (9).

Like several countries in Africa, Mali has been implementing its PPR control and eradication strategy since 2017 with mass vaccination as its main component. Despite the efforts made, vaccine coverage rate remains low, less than 10% (10).

Vaccination in Mali is implemented through a public-private partnership (PPP). The 1990s marked the era of “the privatization of veterinary services,” leading to the gradual disengagement of the government from productive and commercial activities and the government is now refocusing on public service (11). Since then, the country has embarked on a policy of partial cost recovery of vaccination by farmers. Exceptions occur in areas requiring humanitarian support due to environmental disasters or conflict, when a vaccine is further subsidized or even provided free of charge to livestock farmers by development organizations. Twenty years later, the animal health situation in Mali is still fragile. The low vaccination coverage rates for all livestock diseases and the limited networks of private veterinarians are indicators of the inadequate performance of veterinary services. In Mali, the “Ovipeste” vaccine (Nigeria/75/1), produced by the Central Veterinary Laboratory (LCV) in Mali (12) is used. The vaccine is mostly packaged and distributed in multidose vials 100 doses and requires strict cold storage throughout until use. The lack of proper cold chain infrastructure is a major cause of failure in most vaccination programs, especially in countries with very high temperatures like Mali (13). It is often impossible to keep vaccines cold when travelling long distances in rural areas and lack or failures of electricity. Without strong vaccine monitoring and conservation along the supply chain, there is high risk of vaccine wastage, translating to economic losses and inefficiencies in vaccination. In 2005, the WHO estimated that approximately half of the vaccines produced globally are wasted and therefore recommended that countries strengthen local vaccine wastage monitoring (14).

Few studies attempt to estimate the vaccine wastage rate in livestock in sub-saharan Africa because of variability in production systems and challenges in data availability. In Mali, no study has been conducted to estimate vaccine wastage rate recorded during annual livestock mass vaccination campaigns. This is important to inform vaccine actors how to optimize vaccination campaigns by limiting vaccine wastage. It is also recommended that the vaccine wastage rate be evaluated at the same time as the vaccination coverage rate for a better appreciation of the wastage rate (14).

This present study was therefore conducted to estimate the wastage of PPR vaccine along the supply chain for the 2023 vaccination campaign, for improved control of PPR and other SR diseases.

Vaccine transport, storage, and use highlights

Vaccines are primarily transported from supply sources to storage or vaccination sites using coolers, although, these containers have limited capacity to effectively maintain the cold chain (26). Depending on the distribution level, vaccines are transported over distances ranging from 11 km to more than 400 km with significant difference for regional actors, due to the considerable separation between regional capitals and Bamako, the national capital. They typically require a minimum of 4 h, while those operating at intermediate or field levels generally take 1–2 h, despite covering shorter distances. This is largely due to factors such as the modes of transportation, primarily motorcycles, and poor road conditions, which can prolong transit time for field-level personnel. Interestingly, the cost of ice used to preserve vaccines during transport is relatively uniform across all distribution levels, ranging from USD 0.6 to 1.9 per trip for most cases. However, given the disparities in vaccine volumes transported, this uniformity suggests a proportionally higher ice cost at the field level. This is likely attributable to longer transport durations and suboptimal transport conditions.

Regarding vaccine storage, only half of stakeholders rely primarily on the electricity supplied by public utilities supplemented by personal solar energy systems. This trend reflects the ongoing energy crisis, with public electricity coverage reaching only 52% nationwide and just 24% in rural areas (41). In particular, central veterinary services that lack functional solar installations refrain from maintaining vaccine stockpiles, to minimize losses caused by cold chain failure during power outages. The absence of secondary sources of energy is also noted by at least two-third of stakeholders posing a risk to vaccine quality, as cold chain failure may occur without being detected, especially in the absence of a temperature monitoring and recording system. This not only jeopardizes vaccination efficacy but also limits the capacity to accurately estimate vaccine wastage rate linked to cold chain failures.

The study highlighted the limited capacity of vaccinators to cover the target populations. In fact, in one day of vaccination, both private and public vaccinators can only cover two villages corresponding to 10 farmers. This might be due to the spread distribution villages and herd in the context of Mali combining to the low logistics of actors (mean of transport, insufficiency of vaccinators and vaccination materiel). Moreover, accessing certain locations can be challenging due to their remoteness and poor road conditions, particularly during the rainy season. The nature of the vaccine is also a major constraint considering the context. Indeed, a 100-dose vaccine vial typically covers only three farmers considering the small-scale SR herds managed by most of farmers. Consequently, due to the limited time window (maximum 1 h) for using vaccines after vial opening, combined with the logistical challenges of assembling animals and the low number of doses required per herd, only a limited number of animals can be vaccinated from a single vial (33, 42). This constraint leads to considerable vaccine wastage, not only due to denaturation after vial opening but also from residual losses during administration. Efforts should focus on strengthening the logistical capacity of field actors to enable them to vaccinate a larger number of animals per day. This would help shorten the duration of vaccination campaigns, which is crucial for the efficient management of limited resources.

The wastage rates are estimated at 24.3 and 25.4% for the public and private sectors, respectively, resulting in a national wastage rate of 25%. The WHO acknowledges that establishing a universally acceptable vaccine wastage threshold is not feasible, as it varies depending on vaccination programs, local contexts, disease profiles, and vaccine types (14, 43). Studies conducted in various regions on comparable freeze-dried vaccines used in human immunization programs have reported a wide range of wastage rates, varying from 5 to 79% (29, 30, 33, 44, 45). However, few studies have addressed vaccine wastage within the field of animal health. In Ethiopia, for instance, the wastage rate of the PPR vaccine was estimated at 22% (18). Regardless, vaccination coverage remains the most critical factor to consider. The WHO recommends factoring in vaccination coverage when evaluating wastage rates. The correlation between vaccine wastage rate and immunization coverage is crucial for determining whether wastage levels are relatively excessive. Both metrics should be analyzed over time rather than at a single time point to identify trends (14). Based on this approach, the estimated wastage rate of 25% observed in the current study is considered notably high, particularly given the low vaccination coverage of only 10% (10).

Our study shows that wastage is much lower at the central and intermediate levels compared to the field level. Indeed, these levels only cover vaccine transport and storage, and the wastage occurs mainly with unopened vials (29, 33, 45, 46). In contrast, wastage at the field level predominantly results from factors such as denaturation, improper injection, vial breakage, and reconstitution errors. These four causes alone account for at least 97% of wastage in both the public and private sectors. Wastage is mainly recorded during vaccine transport, storage, and use, respectively, for actors at the central, intermediate, and field levels. This once again highlights the need to strengthen resource allocation to field actors to improve the implementation of vaccination campaigns.

Denaturation is one of the main factors contributing to vaccine wastage in this study. It can be attributed to the short timeframe for vaccine use after reconstitution (typically 1 h), small flock sizes, and the logistical challenges of assembling animals for vaccination in Mali context (47, 48). Numerous studies have shown that the wastage rate of freeze-dried vaccines is significantly higher than that of liquid vaccines, primarily due to their greater susceptibility to denaturation once opened (29, 33, 49). Unfortunately, only honest actors are likely to adhere to this deadline because a denatured vaccine cannot be differentiated from a normal vaccine at first sight. A vaccinator could easily mislead farmers and continue administering vaccines in order to maximize personal profit. This highlights the importance of vigilance among farmers when using this type of vaccine. Their active participation in vaccine quality control is crucial, especially when dealing with vaccinators who may have limited training. Moreover, many vaccinators shift the burden of vaccine wastage onto farmers by charging them for the full cost of a 100-dose vial, regardless of the number of animals vaccinated. They administer doses to the available animals and discard the remaining volume. This type of wastage often goes unnoticed at the national level. As a result, some vaccinators may report the number of doses paid for rather than the actual number of animals vaccinated, leading to distorted estimates of vaccination coverage. A practical, though not necessarily cheaper, alternative would be to use vials with fewer doses to help minimize such wastage (5, 44). Wastage can also be reduced by organizing sessions with large numbers of animals (grouping herds), so even if the last vial used has doses remaining, it is a small proportion of the doses distributed during the session.

Vaccine wastage during injection is frequently associated with the vaccinator’s level of experience and the adequacy of animal restraint. Despite the high level of education of the respondents, it is essential to provide thorough training to vaccinators, particularly when involving inexperienced vaccinators and community-level personnel with limited technical backgrounds. Similar attention should be given to procedures related to vaccine reconstitution, which can also be a significant source of wastage.

Vial breakages are frequently observed due to inadequate transport conditions, particularly when vaccines are carried in coolers where ice packs and vaccine vials are placed haphazardly, which is common in the context of Mali. This increases the risk of impact between the ice packs and the vials, leading to breakage (26). Additionally, some actors store the vaccine in freezers at −20 °C, as recommended by the manufacturer for long-term storage (up to 2 years) (12). However, the vials often become frozen solid, increasing the risk of damage, especially during removal if handled carelessly.

Cold chain failures appear to be a minor contributor to vaccine wastage in contrast to the conclusions reported by Michel et al. (13). In the public sector, only 3.1, 9.4, and 5.3% of respondents reported experiencing cold chain failure during transport, storage, and field use, respectively. Similarly, in the private sector, 4.0, 5.3, and 1.4% of respondents reported such failures during the same phases. Moreover, cold chain failures contributed minimally to overall vaccine wastage, accounting for only 0.4 and 0.5% in the private and public sectors, respectively. Although there is an important risk of underestimating the wastage related to cold chain failure (see study limitations in the following section), this wastage deserves to be seriously considered in vaccination programs. As precautionary measure, it is essential to transport vaccines using insulated containers with tight-fitting lids. When lined with ice packs, these containers help maintain the required cold temperatures for both vaccines and diluents during transport and/or temporary storage (26). Moreover, the use of thermotolerant vaccines offers a significant advantage in hot and arid regions such as Mali, where cold chain infrastructure is limited and where recent electricity shortages have further exacerbated storage challenges (13, 50, 51). For instance, the PPR thermotolerant vaccine developed by the International Livestock Research Institute (ILRI), in collaboration with Mali Central veterinary laboratory (LCV) and Hester Biosciences, can be stored or transported at 32.5 degrees Celsius for 9 days (52). Additionally, it remains viable for up to 5 h after reconstitution (53), which greatly reduces wastage related to denaturation, previously accounting for 46.0 and 32.4% of field wastage in the private and public sectors, respectively.

The limitation of this study is the approach used to estimate the wastage due to cold chain failure. The findings were based on a cross-sectional study relying on self-reported data collected during interviews. Since temperature fluctuations were not directly monitored, cold chain-related wastage may be underestimated, as breaches can occur without the knowledge of those managing the cold chain. This concern is particularly relevant in the current context in Mali, where there are frequent power outages, the lack of backup power sources for most actors, the long distances of vaccine transportation and the use of inadequate vaccine coolers during transport might further compromise cold chain integrity. Besides, Dione et al., have raised concerns about the quality of vaccines delivered to farmers in Mali regarding the low capacity of veterinarians to store the vaccine at required temperatures (48). More rigorous approaches should be used to better estimate the wastage due to cold chain failure by recording the temperatures through all levels of the PPR vaccine distribution over the time. Moreover, implementing a reliable temperature monitoring and recording system is a critical component of PPR control and eradication strategies, even in developed countries. For instance, a temperature monitoring study conducted by Young et al. (26) for a month in India, the vaccine supply system showed significant peaks in temperatures (above 10 °C). A study conducted by Scott and Shannon (54) in the United States on the supply chain of animal health products showed that only a third of the refrigerators of the distributors tested operated within the acceptable temperature range. Among those who claimed to monitor temperatures, some relied solely on subjective assessment, such as noting that the vaccines felt “cool” upon removal, rather than using proper thermometric equipment. Even inside a freezer, temperature variations can occur depending on the specific location where the vaccines are stored (55).

This study revealed a high vaccine wastage rate during PPR vaccination in Mali, at the same time as low vaccination coverage. Wastage primarily occurs at the field level through denaturation, improper injection, vial breakage, and reconstitution errors. Such wastage poses a significant challenge to the PPR control strategy, which heavily relies on mass vaccination. To mitigate field-level wastage, it is essential to implement several measures: adopting vials that contain fewer vaccine doses per vial, using vaccines with longer stability post-reconstitution, promoting thermotolerant vaccines, enhancing vaccinator training, and improving the organization of vaccination campaigns. Additionally, regular temperature monitoring and recording are crucial for better management cold chain-related wastage.