The first days of Pfizer Inc's Covid-19 vaccine rollout have seen unexpected hitches including some vaccines being stored at excessively cold temperatures and Pfizer reporting potential challenges in its vaccine production, US officials said on a Wednesday press call.

At least two trays of Covid-19 vaccine doses delivered in California needed to be replaced after their storage temperatures dipped below minus 80 Celsius), US Army general Gustave Perna said on the call. Pfizer's vaccines, made with partner BioNTech SE, are supposed to be kept at around minus 70C...