How does Colombia package vaccines between -15ºC and -50ºC

Dear all,

I want to share with you the experience about packaging vaccines that require to be between -50ºC and -15ºC to maximize the shelf life given by the lab.
We prepared a 40% solution of Mono Ethylene Glycol with water inside HDPE bottle (icepacks), freezing at -50ºC for 2 days at least, then we put 34 HDPE bottles around the vaccines inside of a cold box of polyestyrene with thickness of 5 cm.
This packaging warranties for 24 hours, enough to delivery in 38 departments, states or districts.