I used to work for a biotech company that shipped products at -70, -20 (normal freezer) and 2-8 (refrigerated). It's normal to ship using dry ice or refigerated gel packs. It's generally a cheaper alternative than temperature controlled containers but comes at the risk that a delayed shipment will result in the product becoming too warm at so will likely need to be thrown out. If you're interested you can google "active vs passive cold chain logistics" and you'll find lots of articles discussing the pros and cons of both and how to decide which one is right for your product.

I can't guarantee that Pfizer isn't cutting corners but nothing they are doing here is sounding any alarm bells to me