May 5 (UPI) -- U.S. pharmaceutical conglomerate Pfizer and German partner BioNTech announced Tuesday they have begun administering a potential COVID-19 vaccine to human test subjects in the United States.
The companies said they administered the experimental "BNT162" vaccine in the first U.S. patients at various sites, including New York University, the University of Maryland and Cincinnati Children's Hospital. Eventually, more than 300 U.S. participants will receive the vaccine as part of the study.
The initial trial is designed to determine the safety, immunogenicity and optimal dose level of four versions of Pfizer's vaccine candidate, which uses "messenger DNA" to spur the body to produce antibodies that fight the coronavirus.
The companies said they have been moving quickly in the process. They first began human trials in Germany last week.
"The short, less than four-month time frame in which we've been able to move from pre-clinical studies to human testing is extraordinary and further demonstrates our commitment," Pfizer CEO Albert Bourla said.
The companies said they're preparing a large-scale rollout that will produce millions of vaccine doses this year and hundreds of millions next year.
Pfizer's vaccine candidate is one of eight that are now in the clinical trial stage as drugmakers search for immunity against the virus that's so far killed 250,000 worldwide.
A phase-one safety study of Moderna's "mRNA-1273" vaccine candidate began in March in association with the National Institutes of Health. It could advance to the second stage between now and July and the final phase possibly in the fall.
Other vaccine candidates presently in human trials include include four in China and one each at Oxford University in Britain and pharmaceutical firm Inovio.