SEOUL:South Korea's forensic agency has found no links between a 17-year-old boy's death and a flu shot he had taken, the Yonhap news agency reported, amid rising concerns about the safety of the vaccines following the death of at least 25 people.

The boy was among the first reported to have died as part of a government campaign to vaccinate about 30 million of a population of 52 million to prevent coronavirus complications. The toll has grown to 25 over the past week, sparking calls from doctors and politicians for a halt to the programme.

Health authorities have refused to suspend the campaign on Thursday, citing a lack of evidence to suggest direct links between the deaths and the vaccines.

The National Forensic Service has been conducting autopsies on some of the deceased as part of a government investigation, and determined that the 17-year-boy's death had no relations with the vaccine, Yonhap said, citing police.

Both the forensic agency and police were not immediately reachable for comment.

Of the 25 cases, 22 including the boy received a free flu shot the government has allotted for some 19 million teenagers and senior citizens, according to the Korea Disease Control and Prevention Agency (KDCA). At least seven of the nine people investigated had underlying conditions.

Vaccine providers include domestic firms such as GC Pharma, SK Bioscience, Korea Vaccine and Boryung Biopharma Co. Ltd., a unit of Boryung Pharm Co. Ltd., along with France's Sanofi. They supply both the free programme and paid services.

Ten people received products from SK Bioscience, five each from Boryung and GC Pharma, four from Sanofi and one from Korea Vaccine.

It was not immediately clear if any of the vaccines made in South Korea were exported, or if those supplied by Sanofi were also being used elsewhere.

All four domestic firms declined to comment, while Sanofi did not respond to requests for comment.

South Korea ordered 20% more flu vaccines this year to ward off what it calls a "twindemic" of concurrent major flu and COVID-19 outbreaks in winter.

The KDCA reported 155 new cases as of Thursday midnight, for the second consecutive day the daily tally marked a triple-digit increase after largely hovering below 100 over the last two weeks. It brought the total infections to 25,698, with 455 deaths.

So far 8.3 million people had been inoculated since the programme began on Oct. 13, with about 350 cases of adverse reactions reported, the KDCA said.