Vials with a sticker reading, "COVID-19 / Coronavirus vaccine / Injection only" and a medical syringe are seen in front of a displayed Pfizer logo in this illustration taken October 31, 2020. (Photo: REUTERS/Dado Ruvic)

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

Pfizer last week released initial data on its vaccine developed with German partner BioNTech that showed it to be more than 90% effective.

On Monday, rival Moderna 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.