Pfizer Inc said on Tuesday that along with partner BioNTech Se it was developing a booster shot to protect against Covid-19 variants.
"We are already laying the groundwork to respond quickly if a variant of SARS-CoV-2 shows evidence of escaping immunity by our vaccine," Pfizer said in an email to Reuters.
However, the company added that studies needed to evaluate the booster shot are yet to be determined in agreement with regulators.
The story was first reported by Bloomberg News.
Moderna Inc, whose vaccine has also been authorized for emergency use in the United States, had said on Monday it would test a new booster shot aimed at the South African variant of the coronavirus after concluding the antibody response could be diminished.