Mongolia has restricted entry to all travelers except for nationals and permanent residents of Mongolia; foreign national travelers with a short-term visa (business (B-type), diplomatic (D-type) or official (A-type) visa) issued on or after October 8.
Children under the age of 2 are exempt from presenting a COVID-19 test.
Travelers with proof of recovery from the virus within the last 90 days prior to boarding. Proof of a recent positive viral test and a letter from your healthcare provider or a public health official stating that you were cleared to travel.
More info at the CDC site
Travelers who did not get tested, are advised to stay home and self-quarantine for 10 days after travel.
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