Singapore will freeze new ticket sales for quarantine-free travel in an effort to limit exposure to imported omicron cases, the health ministry said in a statement Wednesday.

The suspension, which begins Thursday and runs through Jan. 20, applies to flights and buses into the city-state.

Travelers who have already booked tickets under Singapore’s vaccinated travel lane arrangements will still be able to enter the country without serving quarantines.

“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.

Singapore has so far detected 65 imported omicron cases. As of Monday, there were six local omicron cases in the country, the health ministry said.

About 96% of Singapore’s eligible population is fully vaccinated, or about 87% of the total population, according to health ministry data. More than a third of the total population (34%) has received a booster. Shots for children between 5 and 11 years old have been approved and are set to begin Monday.

When the ticket sale suspension ends on Jan. 20, the number of people allowed to visit Singapore without serving quarantines will be temporarily reduced, according to the press release.

The health ministry said the Civil Aviation Authority of Singapore and the Ministry of Trade and Industry will provide more details on vaccinated travel lanes via air and land, respectively.

Travelers who enter Singapore under quarantine-free arrangements have to take a PCR test on arrival, and daily antigen rapid tests for the first seven days in the country.

Singapore’s vaccinated travel lane program was key in the country’s pivot to a “living with Covid” strategy, reopening borders while keeping certain anti-virus measures in place. Freezing new ticket sales for this arrangement appears to be the biggest yet scale back of that effort.

Since omicron emerged, the government has tightened testing measures for travelers and postponed the launch of quarantine-free travel lanes with Qatar, Saudi Arabia and the UAE. Singapore has also restricted travel from African countries including South Africa, which first detected the omicron variant.