The head of BioNTech SE, the German company that developed the first Covid-19 vaccine, said a new formula is likely to be needed by mid-2022 to protect against future mutations of the virus.

Ugur Sahin, co-founder and chief executive officer of BioNtech, told the Financial Times that while current variants of Covid-19, such as the contagious delta strain, were not different enough to undermine current vaccinations, new strains will emerge that can evade booster shots and the body’s immune defenses.

“This year [a different vaccine] is completely unneeded, but by mid-next year, it could be a different situation,” he said. “This is a continuous evolution, and that evolution has just started.”

BioNTech partnered with U.S. pharmaceuticals giant Pfizer Inc. to develop its Covid-19 vaccine. Last month, the companies submitted initial data to U.S. regulators about the use of the vaccine in children aged 5 to 11, one step closer to bringing shots to school-age kids.