The emvolio.gov.gr vaccination platform opened on Wednesday for people aged between 70 and 79 years old to book an appointment for their second booster shot against Covid-19.
The 60-69 contingent comes next, with appointments for that age group being available on the platform as of Friday.
As was the case with the first booster, citizens can choose between the Pfizer and Moderna vaccines.
Some 40,000 appointments have already been booked for the fourth dose of the vaccine in the 80+ age group, after the platform opened for them last Thursday.
Health authorities estimate that around 1.3 million citizens over the age of 60 are entitled to a second booster shot, which needs to come at least four months after the first booster.
A fourth dose is not mandatory, but it is strongly recommended for the elderly and people with health problems that may make them more vulnerable to serious illness.