The move applies to all 24 countries with which Singapore has agreements for quarantine-free air travel, as well as overland bus services with Malaysia, the government said Wednesday. People who already have tickets will be able to travel.

Singapore will also temporarily reduce quotas and ticket sales for travel after Jan. 20, the Ministry of Health said.

“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 ministry said in a statement.

Omicron has fast become the dominant COVID-19 strain in many countries since it emerged about a month ago, accounting for more than 70% of cases in the U.S. alone. The variant has been found in Singapore, which has been opening its borders to select countries since October after abandoning a COVID-Zero approach still pursued by the likes of China and Hong Kong. 

Singapore Airlines Ltd. fell as much as 1.6% after the announcement.  

Singapore is now also instructing people returning from overseas to avoid high-risk mask-off activities such as dining at restaurants or exercising in gyms for seven days after arrival, even if they test negative each day. Previously, returnees were allowed to move freely once they tested negative.

Singapore’s local cases have plunged from a daily high of more than 4,600 in late October to just 221 on Dec. 21, according to Ministry of Health data. Still, imported cases—most of them omicron—are on the rise to more than 50 each day.

Singapore is one of the most vaccinated places in the world, with 96% of those eligible and 87% of the population overall fully inoculated. More than a third of the population has received booster shots. Jabs for those under 12 years of age will start on Dec. 27.