SINGAPORE, Dec 22 (Reuters) - Singapore will freeze all new ticket sales for flights and buses under its programme for quarantine-free travel into the city-state from Dec. 23 to Jan. 20, the government said on Wednesday, citing risk from the fast-spreading Omicron COVID-19 variant. Under the vaccinated travel lane (VTL) programme, Singapore allows quarantine-free entry from some countries to fully vaccinated travellers on designated flights or buses. The travellers have to undergo regular testing. Singapore has set up these lanes for about two dozen countries, including Australia, India, the United Kingdom and the United States. The government said it will also temporarily reduce the VTL quotas and ticket sales for travel after Jan. 20, 2022. For flights, the total ticket sales will be capped at 50% of the allocated quota. "Our border measures will help to buy us time to study and understand the Omicron variant, and to strengthen our defences, including enhancing our healthcare capacity, and getting more people vaccinated and boosted," the health ministry said in a statement.