Vaccine Distribution Logistics.

Lyophilized vaccines are typically stored in cold rooms and refrigerators and transported in cold boxes through a 2-8°C cold chain, with a few exceptions, such as those containing Varicella that may be transported at -50°C to -15°C. Vaccines stored as liquid formulations also require a 2-8°C cold chain, while frozen vaccines are stored in freezers at around -20°C or ultralow -80°C freezers. These require cold chains, with cold boxes containing frozen gel packs or preconditioned phase-change materials (PCMs), or insulated boxes with dry ice (e.g., BioNTech's COVID-19 mRNA vaccine). Cryopreserved vaccines require liquid nitrogen (LN2) vapor phase (LNVP) freezers and cold chains that use Dewars with LN2 or LNVP dry shippers. Storage and distribution methods for all vaccines follow strict national and international guidelines and regulations, maintain an end-to-end chain of custody, and are monitored by temperature data loggers and other devices. Different distribution models are employed for different products and by different countries, ranging from the hub-and-spoke model for LNVP distribution to models with several intermediate stops. Storage and distribution of lyophilized, frozen, and cryopreserved vaccines are described.