KATHMANDU, Dec 24 (Reuters) - Bhutan has started giving COVID-19 booster shots to senior citizens and priority groups as the Himalayan kingdom tries to stave off the Omicron variant, health ministry officials said on Friday. Those aged 65 and older, overseas travellers, health workers, sufferers from chronic ailments and all adults living in "high risk" areas are eligible, the officials said. "Bhutan becomes the first country in the South Asian region to administer booster doses," public service broadcaster BBS said in a report. Officials said Bhutan planned to inoculate more than 228,000 people in a week. "As we did for the second dose, mix and match is recommended even for the booster, given its higher efficacy," Sonam Wangchuk, an official of the Royal Centre for Disease Control (RCDC), was quoted as saying in the Kuensel newspaper. Bhutan has not reported any cases of Omicron variant so far and the RCDC regularly sequences samples from across the country to watch for any signs of an "incursion", officials said. The nation of about 750,000 people says it has vaccinated more than 93% of people older than 12 with a second vaccine dose. Nestled between China and India, Bhutan has been able to slow the spread of the virus through measures such as early screening and monitoring at entry points, testing and sealing its borders. It has announced just three deaths linked to COVID-19 and 2,659 infections since the pandemic started.