Pfizer Inc. and partner BioNTech SE plan to start testing soon a freeze-dried version of its Covid-19 vaccine, which if proven to work safely could ease storage and handling of the shots in rural US areas and low-income countries.In April, Pfizer is set to launch a clinical trial evaluating a so-called lyophilized formulation in adults 18 to 55 years old in the US., according to a government database, clinicaltrials.gov, and confirmed by the company.The 1,100-subject study would last roughly two months, with researchers seeking to determine whether the processed version is as safe and effective as the version authorized by regulators beginning late last year. Researchers would administer to subjects either the processed version or the current formulation.