The public health authorities said Thursday that they have confirmed five more "breakthrough infections” among fully vaccinated people, pushing the total to nine.

All of the breakthrough infections occurred in people who have received the Pfizer vaccines. Authorities are also investigating whether the new breakthrough cases are variant viruses. Health officials categorize Covid-19 infection cases within 14 days of completing vaccination as breakthrough infection.

"The figure accounts for about 0.0004 percent of 2,143,385 people who have completed vaccination," a health official said. "Among the 1,039,559 people who completed the vaccination and passed the 14 days for immunity was 0.87 per 100,000."

The official noted that the figure is much lower than that of the U.S., where the breakthrough incidence is 10.2 per 100,000 people.

The Central Disaster and Safety Countermeasures Headquarters called for people to follow the quarantine rules, such as wearing masks, keeping distance, and maintaining sufficient ventilation, even after vaccination.

Noting that AstraZeneca's Covid-19 vaccine reservations are coming to a close on Thursday, the headquarters said that at the current rate, it is possible to achieve its goal of inoculating 13 million people within the first half of the year.

"As of midnight Wednesday, the reservation rate for the elderly has risen to 77.6 percent," Ministry of Health and Welfare Spokesperson Son Young-rae said. "By age, reservation rate for those aged 70 to 74 have risen to 80.7 percent, those aged 65 to 69 to 79 percent, and those aged 60 to 64 to 79.4 percent.

As the reservation will continue until midnight Thursday, the government expects that the reservation rate will increase further, he added.

"If the vaccination proceeds without any setbacks by the end of June, we will be able to achieve initial targets," he said. "Also, 80.3 percent of teachers at kindergartens, daycare centers, and low elementary grade – first and second grade -- have also made reservations."

Korea has vaccinated 6,741,993 people – 4,296,043 with the AstraZeneca vaccine and 2,445,950 with Pfizer's vaccine – with the first shot of the vaccine up 403,780 from the previous day. The figure accounts for 13.1 percent of the country's population.

As the vaccine rollout among the elderly population gains pace, social distancing guidelines were partly eased for vaccinated people Tuesday.

While up to eight immediate family members are currently allowed to gather, those who have received at least one shot of Covid-19 vaccines are exempted from the distancing rule.

Authorities plan to ease virus curbs further next month if the average number of new daily cases stays below 1,000 amid the vaccine rollout.

From July, people who have gotten their first shots will be allowed to take their masks off outdoors and will get discounts on fees at major public facilities, they said.

On Thursday, the Korea Disease Control and Prevention Agency confirmed 681 new cases, including 672 local infections, raising the cumulative caseload to 142,157.

Three more people died of the Covid-19, raising the death toll to 1,968 with a fatality rate of 1.38 percent, and a total of 132,699 people have returned to their daily life after full recovery, up 631 from the previous day. The country has carried out 9,872,324 tests since Jan. 3 last year.