Moon, who presided over a Covid-19 response meeting, said that the country's pandemic situation got serious amid the higher number of new infections, severe cases and deaths, as well as fewer hospital beds for severe patients.
The government launched the "Living with Covid-19" rules in November to alleviate anti-virus measures following the country's full vaccination rate topping 70 per cent, Xinhua news agency reported.
With the eased social-distancing guideline, the confirmed cases surged for the past month. In the latest tally, South Korea reported 3,309 more cases of Covid-19 for the past 24 hours, lifting the total number of infections to 444,200.
The number of infected people who were in a serious condition surpassed 600, while 32 more deaths were confirmed, leaving the death toll at 3,580.
Moon said it would be important to inoculate the unvaccinated, emphasising the need for the third dose of Covid vaccine.
"A third dose is not an additional shot but a basic shot. The way of thinking needs to be changed that the vaccination can be completed only after receiving the third jab," said Moon.
Moon called for parents to let children aged between 12 and 17 get vaccinated, instructing officials to rapidly review the possible inoculation of minors aged between five and 11.
Over 90 per cent of adults aged 18 or higher was fully vaccinated, while the percentage of children aged between 12 and 17, who got inoculated, remained low as parents refrained from it on fears about possible side effects.
Moon ordered officials to secure more hospital beds for severe patients and move up the date of introducing pills for Covid-19 treatment, originally scheduled for February next year.