The reservation rate for COVID-19 vaccines among people between the ages of 18 and 49 has been lower than expected, creating an obstacle in the government’s plan to achieve herd immunity by November.

According to the Central Disease Control Headquarters, the vaccine reservation rate for the age group, about 15.37 million people, was 61.3 percent as of Thursday at midnight.

Online reservations for the age group opened on August 9 with a 10-day rotational booking system, in which people could reserve their shots on designated days based on the last digit of their birth date.

After one full cycle of the 10-day rotational period, only 9.43 million people have signed up for their jabs so far.

Compared to the previous 80.7 percent vaccine reservation rate for people aged 60 to 74, the figure for the younger age group was lower than the health authorities’ expectations. The government, however, explained that the inoculation rate will turn out higher than the reservation rate.

“In the case of people aged 18 to 49, if we consider that many of them have already received inoculations as they were included in various priority groups, the actual participation rate is estimated be about 77 percent of the age group,” Kwon Jun-wook, head of the Korea National Institute of Health, said in a briefing Friday.

Amid the more contagious delta variant becoming the dominant cause of infections and vaccines seeing a lower prevention rate against the delta variant, there are growing concerns over whether the vaccination rate goal should be higher in order to achieve herd immunity.

“The government initially proposed to achieve herd immunity by completing full vaccination of more than 70 percent of the people by November, but we should continuously review the objective for the vaccination rate as we reflect the spread of the delta variant and the virus‘ reproduction rate,” Kim Ki-nam, an official at the government’s COVID-19 vaccination response task force, said earlier this week.

He added that the primary goal now is to achieve a 70 percent full vaccination rate as early as possible and the government will consider the vaccination rate needed for herd immunity afterwards.

The government has reaffirmed its goal to reach a 70 percent first-round vaccination rate before the Chuseok holiday, which is slated to begin September 20, and achieve herd immunity with a 70 percent second-round vaccination rate before November.

For those in the younger age group who missed their date to book a shot, there are additional opportunities.

People aged 36 to 49 are currently allowed to make reservations until 6 p.m. on Friday. Those aged 18 to 35 can book their shots from 8 p.m. on Friday to 6 p.m. on Saturday.

Everyone in the age group will be given another chance to make reservations over the period of almost a month from 8 p.m. on Saturday until 6 p.m. on September 18.

Nationwide inoculations are scheduled to begin next Thursday and continue until September 30.

As there were delays in the supply of vaccine shipments from Moderna, the government said people who make their reservations between August 26 and 29 will receive Pfizer’s vaccine. After that, individuals will be notified of which vaccine they will be inoculated within a week.

According to the Korea Disease Control and Prevention Agency’s latest data, the first-round vaccination rate reached 48.3 percent, while 21.6 percent of the population has been fully inoculated.