Feb. 25 (UPI) -- Researchers at Pfizer-BioNTech announced Thursday that they have started a new clinical trial designed to assess whether a third dose of their COVID-19 will bolster the protection it offers against new virus strains.
The new trial will draw upon participants in the phase 1 study of the vaccine in the United States, who will be offered a booster six to 12 months after receiving their initial two-dose regimen, company officials said.
The study is part of the companies' "clinical development strategy to determine the effectiveness of a third dose against evolving variants," including those first identified in England and South Africa, they said.
It will focus on a new construct of the existing Pfizer-BioNTech vaccine based on the B.1.351, or South African, lineage of the coronavirus, which was first identified last fall, according to the officials.
"While we have not seen any evidence that the circulating variants result in a loss of protection provided by our vaccine, we are taking multiple steps to ... be ready in case a strain becomes resistant," Pfizer chairman and CEO Albert Bourla said in a statement.
"This booster study is critical to understanding the safety of a third dose and immunity against circulating strains," he said.
The new study will include 144 participants age 18 to 85, the companies said.
Participants will be assessed at the time they receive the third dose, then one week and one month later.
As originally planned during the initial clinical trials, participants will continue being followed for up to two years to assess the safety of the shots.
Earlier this week, U.S. health officials attending the CDC's National Forum on COVID-19 Vaccines said a key goal was to "out-vaccinate the variants," or create widespread immunity to the virus within the general population before new strains take hold.
The fear is that new strains may be more contagious, cause more severe illness and be less susceptible to the vaccines, they said.
Officials at Moderna, makers of the other COVID-19 vaccine approved for use in the United States, on Wednesday announced plans to study a booster for the South African variant.
"We want to be prepared for different scenarios," BioNTech CEO and co-founder Ugur Sahin said in a statement.
"The flexibility of our proprietary mRNA vaccine platform allows us to technically develop booster vaccines within weeks, if needed," Sahin said.