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Logistics is a problem because the mRNA vaccines need deep-freezing. The vaccine from Pfizer/BioNTech needs to be stored at −70ºC. The Sputnik V vaccine also needs to be stored at -18ºC. The developing nations may be having the facilities to store the vaccine at such low temperatures, but we can't expect the poorer nations to have tens of thousands of such deep-freezers. And it's not just storing. Transporting the vaccine at such low temperatures can also be a problem.
That's the exact problem that my country is facing right now besides being incompetent, there is no storage facility that is going to cater the right temperature and the only ones don't even meet the exact number. Transport to provinces is problematic but it can be managed.