Pfizer and BioNTech said they would soon seek authorization from regulators for a third dose of their COVID-19 jab to be administered in the United States and the European Union.
The move comes amid fears that the delta variant is behind the latest outbreaks in Asia and Africa and rising cases in Europe and the US.
The drugmakers said a third shot of their COVID-19 vaccine could boost immunity against more contagious variants.
The companies said they were also working on developing a jab specifically against the delta variant.
Shortly after the announcement, the US Food and Drug Administration and the Centers for Disease Control and Prevention said: "Americans who have been fully vaccinated do not need a booster shot at this time. We are prepared for booster doses if and when the science demonstrates that they are needed."