US pharmaceutical firm, Pfizer Inc. has launched a pilot delivery programme for its experimental Covid-19 vaccine in four U.S. states, as the drugmaker seeks to address distribution challenges facing its ultra-cold storage requirements.

Pfizer’s vaccine, which was shown to be more than 90% effective in preventing the virus based on initial data, must be shipped and stored at -70 degrees Celsius, significantly below the standard for vaccines of 2-8 degrees Celsius.

"We are hopeful that results from this vaccine delivery pilot will serve as the model for other U.S. states and international governments, as they prepare to implement effective Covid-19 vaccine programmes,” Pfizer said in a statement on Monday.

It picked Rhode Island, Texas, New Mexico, and Tennessee for the program after taking into account their differences in overall size, diversity of populations, immunization infrastructure, and need to reach individuals in varied urban and rural settings.

The four states will not receive vaccine doses earlier than other states by virtue of the pilot, nor will they receive any differential consideration, Pfizer said.

The company expects to have enough safety data on the vaccine from the ongoing large scale late-stage trials by the third week of November before proceeding to apply for emergency use authorization (EUA).

Pfizer and its partner BioNTech SE have a $1.95 billion deal to supply 100 million doses of the vaccine to the U.S. government, which has an option to acquire up to an additional 500 million doses.

Earlier on Monday, rival Moderna Inc said its experimental vaccine was 94.5% effective in preventing Covid-19 based on interim data from a late-stage trial, boosting hopes that vaccines against the disease may be ready for use soon.

Both the Pfizer and Moderna vaccines use a new technology called synthetic messenger RNA to activate the immune system against the virus.