Health authorities cautioned inevitable setbacks in the vaccination timetable should six million doses of the Moderna vaccine the U.S. firm had promised to deliver this week fail to arrive.

Hong Jeong-ik, an official with the vaccine task force, made the statement Wednesday, adding that it would be difficult to inoculate without vaccines. 

The government earlier had said Moderna promised to provide seven million doses by this coming Sunday, but none have been received since a shipment of one-point-one million doses on August 23.

With no additional doses, it is unlikely that the government goal of vaccinating 70 percent of the population with at least their first shot before the Chuseok holiday will be achieved.

Separately, South Korea will receive more than one-point-five million doses of mRNA vaccines from Romania starting on Thursday.

The government said even without the batch from Romania, if the pledged Moderna volume arrives in a timely fashion, vaccinating 36 million people with their first dose before Chuseok is possible.