Pfizer has launched a pilot delivery program for its experimental Covid-19 vaccine in four US states, as the drugmaker seeks to address distribution challenges posed by its ultra-cold storage requirements.

The US drugmaker said it had selected Tennessee, Rhode Island, Texas and New Mexico for the program because of their differences in overall size, diversity of populations and immunisation infrastructure, as well as the states’ need to reach individuals in varied urban and rural settings.

“The four states included in this pilot program will not receive vaccine doses earlier than other states by virtue of this pilot, nor will they receive any differential consideration,” Pfizer said in a statement.

“We are hopeful that results from this vaccine delivery pilot will serve as the model for other US states and international governments, as they prepare to implement effective Covid-19 vaccine programs.”

A week ago, Pfizer released initial data on its vaccine developed with German partner BioNTech SE that showed it to have an efficacy of more than 90%.

Pfizer’s vaccine must be shipped and stored at -70 degrees Celsius (-94°F), significantly below the standard for vaccines of two-to-eight degrees Celsius (36-46°F).

Earlier on Monday, rival Moderna Inc said its experimental vaccine had 94.5% efficacy 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. Moderna’s vaccine does not require ultracold freezing, a factor that could prove to be major advantage over Pfizer’s product.

What does the Moderna vaccine mean for the fight against Covid?

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