To achieve the full effect of immunization, high vaccine coverage and low vaccine wastage are important. High vaccine wastage makes vaccines less available for use, especially in remote areas where access to the central vaccine storage facility is difficult. To avoid compromising any efforts to increase vaccination coverage while minimizing vaccine wastage (26), an appropriate and accurate demand forecasting of vaccines for the immunization target populations and regular monitoring of vaccine waste at all levels is important. The WHO guidelines on VWR per vaccine (27) recommend 50% VWR for BCG, 10% for OPV, 25% for 10–20 dose vials lyophilized vaccines, 15% for 10–20 dose liquid vaccines, and 5% for single-dose vaccines. Country-specific vaccine procurement and management capacities are essential for achieving such targets. In Cameroon, the targeted VWR (21) under the routine EPI during 2016 and 2017 was influenced by the government’s commitment to more resources in the EPI program, such as setting up a comprehensive multiyear plan (28) and the supplementary immunization activities in health districts with poor performance indicators. Such government efforts led to high vaccination coverage in December 2016 and January 2017.
In the Littoral Region of Cameroon, lyophilized vaccines showed a higher VWR, although within the WHO projected ranges. This finding is similar to that of an existing study in The Gambia (10), which showed higher wastage rates in lyophilized vaccines than in other types of vaccines. The VWR in our study was lower than in a study in Bangladesh (29), where the wastage rate for BCG was nearly 84.9%, followed by the MR vaccine at 69.7%, and PENTA at 44.4%. Notably, the liquid vaccine IPV also showed a high wastage rate (17.9%). This may be because it was introduced into the EPI in the Littoral Region in June 2015 (30), and wastage was high at the early stage of vaccine introduction as typically experienced in new immunization programs (31). Our study supports the existing literature on lower wastage rates for vaccines that follow the multi-dose vial policy (MDVP), as seen in other studies from the North West Region of Cameroon (32) and Bangladesh (29).
The MDVP recommendation on the use of opened vaccine vials for up to 28 days, provided the storage conditions are favorable (33), is expected to reduce vaccine wastages (34). However, for lyophilized vaccines (BCG, MR, and YF), their usage is limited to only six hours after reconstitution or at the end of the vaccination session whichever comes first, after which they must be discarded irrespective of the doses that have been used in the vial (35). Thus, vaccine wastage is only avoidable in large enough sessions that last for less than six hours. Therefore, lyophilized vaccines have a higher wastage rate than liquid vaccines (OPV, IPV, PENTA, PCV, and rotavirus vaccines).
Understanding the relationship between vaccination coverage and vaccine waste is important to investigate the reason for vaccine wastage. Analyzing these two variables over time would allow a better understanding of the reasons for vaccine wastage. If vaccines are used to vaccinate the target population per the immunization plan and standard operating procedures for adequate vaccine management, wastage should remain at a minimum, and vaccination coverage should increase. Overall, our study showed a negative correlation between vaccination coverage and vaccine wastage, and causality may be multifaceted. A lower vaccination coverage may not necessarily be due to the unavailability of vaccines or high VWR. Conversely, a low vaccination coverage may cause an increase in vaccine wastage as vaccines can remain in health facilities and get damaged, resulting in an insufficient number of vaccines to immunize the target population. This is explicable as leftover vaccines taken to outreach sites may not return to the cold chain in their optimal conditions (36) and may be discarded. Notably, between October and November 2016, the wastage of all vaccines decreased as the coverage also decreased. This may be due to the lower number of available vaccines, or could also be related to adopting strategies that reduce vaccine wastage but compromise vaccination coverage (6). The former is the most likely cause in the Littoral Region, as no BCG was available even at the central vaccine storage facility in Yaoundé during this study period. The lack of a particular vaccine has a demotivating effect on healthcare workers in organizing vaccination sessions, as they will need to reorganize such sessions when the missing vaccine becomes available. Parents are demotivated to come for vaccination if they are aware that the vaccines are lacking.
Rural areas are characterized by a smaller population size that is sparsely distributed, resulting in conditions that favor a high VWR (34). This is the case with the Littoral Region, where over the two years, rural districts had higher VWR. Compared to the urban health districts that mostly employ a fixed vaccination strategy (where children are brought to health facilities for vaccination), in rural districts, an outreach vaccination strategy is typically applied to reach people living in remote areas with limited access to health facilities. Usually, vaccine vials taken out for this strategy do not return to the vaccine storage facilities if the vaccine vial monitors (small stickers that adhere to vaccine vials and change color as the vaccine is exposed to heat, letting health workers know whether the vaccine can be safely used for immunization) are not in place. Furthermore, the possibility of accidents occurring in rural areas leading to unopened vial breakage is more likely than in urban areas, and less skilled personnel may be involved in the immunization activities (34). Not fully understanding the importance of vaccination due to low educational levels of rural populations often results in their negligent behavior toward meeting the vaccination appointment (17). This often leads to wasting open vials, especially in lyophilized vaccines. Notably, such differences in rural and urban vaccine waste were not significant in a study conducted in Gambia (10). This may be due to enhanced vaccine management and high vaccination coverage in Gambia. In the Littoral Region of Cameroon, attempts are being made to resolve the vaccine wastage problem in rural areas and nearby health facilities by planning immunization sessions more strategically, thus, increasing the vaccinated target population size.
The two major seasons, dry and rainy, in Cameroon have a distinctively different effect on immunization activities. Although the dry season is very dusty, it is favorable regarding weather, road conditions and energy supply. During the rainy season, parents are more likely to miss vaccination appointments, which result in increased vaccine wastage, especially for lyophilized vaccines. This is probably why vaccine waste for BCG, MR, and YF was higher during the rainy season in 2016. However, in 2017, the wastage rate for all vaccines was unexpectedly higher in the dry season. This may be due to the higher ambient temperature in 2017, which may have affected vaccines with inadequate cold chains.
In conclusion, investigating vaccine wastage concerning immunization coverage is important to better understand the reasons for VWR and to plan and design better immunization programs that address the identified challenges. To reduce vaccine wastage in the Littoral Region of Cameroon, emphasis should be placed on rural areas during the rainy season (especially for lyophilized vaccines) and the dry season. Better cold chain systems should be put in place by investing in basic social infrastructure, such as adequate energy sources for field vaccine storage capabilities. To address some of the challenges associated with vaccine cold chain management, efforts are underway to develop vaccines that can tolerate extreme temperatures or be out-of-cold chains for a certain time under monitored and controlled conditions (37). This controlled temperature chain (CTC) is an innovative approach to facilitate vaccine management, aimed at reducing vaccine wastage and reaching at-risk vulnerable populations living in remote rural areas or hard to reach areas with limited cold chain conditions and infrastructure. However, this requires the vaccines to be used in a campaign or special strategy setting and that they can tolerate ambient temperatures of at least + 40°C for a minimum of three days. The vaccines analyzed in this study are currently not available for CTC usage. Furthermore, capacity building of health workers involved in immunization programs is essential. This could include continued community engagement and sensitization, particularly for the rural population, regarding the importance of vaccination. Finally, increasing the size of immunization sessions by facilitating the transportation of vaccines and personnel close to the target population will reduce open vial vaccine wastage. Considering the diverse geographical and climatic characteristics of Cameroon in general and the Littoral Region in particular, better vaccine forecasting with more realistic wastage rates is recommended to prevent the inappropriate supply of vaccines. Further studies are warranted to generate a more comprehensive analysis of vaccine waste across Cameroon and in dynamic climatic changes. This will allow for more refined policy formulation and customized interventions in various settings.