Study: comparing vaccine storage cold boxes in Nepal
A study published in Vaccine X in February 2024 presents an evaluation of freeze prevention of vaccines transported and stored in the WHO-prequalified freeze-preventive cold box (FPCB) in comparison with the current standard cold boxes (SCBs). The evaluation was conducted across five health facilitates in Nepal. The authors find several advantages to the FPCB but suggest that smaller and lighter models would be more appropriate for Nepal’s immunisation needs and similar immunisation programmes globally.
Transportation and storage
“Vaccines lose potency over time, and this loss is temperature dependent.”
The study highlights WHO guidelines for vaccine handling, which recommend “specific storage conditions” to “ensure quality is maintained throughout the vaccine life cycle”. Interestingly, while vaccine vial monitors to identify exposure to heat have been “available for decades”, there are no vial-level indicators for freezing.
Freezing is a particular concern for liquid vaccines with aluminium salt adjuvants, which have increased freeze sensitivity: “freezing can irreversibly damage these vaccines, reducing potency and compromising protective immunogenicity in recipients”.
“The importance of protecting vaccines from freezing will become even more pressing globally as introductions of new vaccines put pressure on already weak vaccine supply chain systems.”
The authors state that, in Nepal, cold boxes are “primarily used” to transport vaccines from “higher cold chain points to health posts”. Vaccine freezing can cause closed-vial vaccine wastage, with “financial implications for immunisation programmes”, or in cases where it goes undetected, can lead to “loss of vaccine potency and efficacy”.
“Freeze prevention at the equipment level mitigates these risks and eliminates the need for shake testing or vial-level freeze indicators, which have not yet proven cost-effective nor been implemented comprehensively.”
SBCs vs FPCBs in Nepal
The study presents the “first real-world evaluation” of a WHO Performance, Quality, and Safety (PQS)-prequalified freeze-preventative cold box (FPCB). Cold boxes have a greater capacity than vaccine carriers and transport vaccines between different levels of the supply chain. This increased capacity means that more vaccines are transported, which therefore presents a greater financial loss if the vaccines freeze.
Qingdao Leff International Trading Company was the first manufacturer to receive WHO PQS prequalification for an FPCB in 2020. The technology comprises a barrier liner between the ice packs and vaccine storage area to prevent direct contact of vials with ice packs.
The Himalayan terrain reportedly poses “major geographical challenges for vaccine distribution, transportation, and storage”. After a shift from a “highly centralised” system to a more decentralised model in 2015, Nepal has faced “both structural and operational issues”, from infrastructural weakness and shortage of skilled staff to delays and lack of coordination. Vaccination coverage “varies considerably across its diverse and geographically dispersed population”.
In response, Nepal has dedicated “significant resources” to improve the service delivery infrastructure of its national immunisation programme”. The authors comment that reaching underserved and widely dispersed populations will “boost vaccine coverage”.
Vaccines in Nepal are “typically” collected and distributed from regional and district cold chain points to health posts once a month for routine immunisations. Further trips are required for vaccination campaigns. Vaccines are transported by the alternate vaccine delivery (AVD) system or health workers. The former involves “local persons engaged in this activity on a part-time basis”, who use cold boxes or carriers in their own vehicles.
Performing to standards
The authors reflect that the primary purpose of the equipment is to prevent vaccines from freezing; in terms of this purpose the FPCB “performed to standards”. The SCBs cooled down “much more quickly” than the FPCBs, thanks to the thermal buffering. While this is “not much of an issue” for extended journeys or temporary storage, the slower cooldown can mean “exposure to elevated temperatures for most of the session” in short outreach sessions. Although the amount and level of thermal exposure is “relatively minimal”, it can be “very noticeable” for health workers trained to keep vaccines within the “acceptable” range: above 0 °C and below + 10 °C.
Additionally, the authors identified a “relatively long period of freezing” in SCBs, which is “not uncommon and can lead to loss of vaccine potency”. Despite “numerous high temperature excursions”, there was no reported incidence of vaccine wastage due to total heat exposure.
“The primary advantage of FPCBs over SCBs is prevention of freezing even when fully frozen, non-conditioned ice packs are used.”
This advantage is expected to “simplify logistics” because if health workers can use fully frozen ice packs, they will need less time to prepare cold boxes. A potential further advantage is a “reduced training burden”. The authors recommend further research and development in pursuit of “smaller and lighter FPCBs relative to their usable storage volume”. Furthermore, investing in FPCBs to prevent the freezing of expensive vaccine shipments would “potentially” be good value as the cost of procuring one FPCB is “much less” than the value of the vaccines that are prevented from freezing.
The paper concludes with recommendations for future research and development, including:
- Explicitly modelling, validating in real-world conditions, and publishing estimated vaccine degradation due to any additional heat exposure from demonstrated longer cooldown periods
- Further product development that might lead to lighter equipment with more storage space and a shorter cooldown period while still thermally protecting vaccine potency from both freezing and heat exposure
Did you read the paper? What useful contributions does it make to vaccine technology discourse? How might the FPCBs fare in your vaccination programmes? For more on novel vaccine technologies and strategies don’t forget to join us in Washington this April for the Congress or subscribe to our newsletters here.