President Sebastián Piñera was present on Monday when two adults with immunosuppression problems received a fourth vaccination for COVID-19 at a Santiago hospital.
Chile is applying a fourth dose early because the current daily infection rate of 4,000 coronavirus cases could rise to 10,000 or more, Piñera said.
Vaccination with a fourth dose for the immunosuppressed will end on Feb. 7. Then the program will turn to people over 55 years old who had a third dose at least six months ago.
Chile, which has 19 million people, had planned to start with the fourth dose in February. The sharp increase in infections in neighboring Argentina, Bolivia and Peru contributed to its decision to advance the process.
Israel approved a fourth vaccine dose for people most vulnerable to COVID-19, an official said on Dec. 30, becoming one of the first countries to do so as it braced for a wave of infections fueled by the omicron variant.