Some of the leading vaccines present their own logistical challenges. Some of the leading vaccines (Moderna, Pfizer) are quite fragile and are hard to transport and store. Moderna needs to be shipped and stored at -20C (-4F) this is tricky but not that hard, since it is in the range of commercial freezers. The Pfizer vaccine needs to be shipped and stored at -70C (-94F) which is outside the range of ordinary freezers (bio labs have them but doctors labs do not). Pfizer can be packed in dry ice to ship, but the ice needs to be replenished every 24 hours. https://twitter.com/LizSzabo/status/1298646754884300800