Starting Monday, the eligibility for the fourth COVID-19 vaccine shot will be expanded to people aged 50 and older as well as people aged 18 and older who have underlying health conditions.

According to quarantine authorities on Sunday, patients and workers at facilities vulnerable to the virus, such as nursing homes and homeless shelters, are also eligible for the second booster shot from Monday.

Currently, people aged 60 and older and people who have an immune disorder are eligible for the fourth COVID-19 vaccine shot.

With the government broadening eligibility for a fourth dose of COVID-19 vaccines, people who were born between 1963 and 1972 can receive the fourth dose 120 days or four months after their third shot.

Those who were infected with the virus after their third shot are also advised to receive the second booster four months after their third shot.

The so-called mRNA vaccines, such as Pfizer or Moderna are recommended for the fourth shot, but people may choose the Novavax vaccine if they want.