CDC, US:

SARS-CoV-2 B.1.1.529 (Omicron) Variant — United States, December 1–8, 2021

“Among these cases of COVID-19 attributed to the Omicron variant, 34 (79%) occurred in persons who completed the primary series of an FDA-authorized or approved COVID-19 vaccine ≥14 days before symptom onset or receipt of a positive SARS-CoV-2 test result, including 14 who had received an additional or booster dose; five of the 14 persons had received the additional dose <14 days before symptom onset.”

WHO:

WHO Urges Nations To Lift Travel Bans & Not Mandate 'proof Of Vaccination' For Entry

WHO bats against international travel bans

In its recommendation, WHO urges its member nations to lift or ease international traffic bans as they do not provide added value and continue to contribute to the economic and social stress on the nations. "The failure of travel restrictions introduced after the detection and reporting of Omicron variant to limit the international spread of Omicron demonstrates the ineffectiveness of such measures over time. Travel measures (e.g. masking, testing, isolation/quarantine, and vaccination) should be based on risk assessments," stated WHO in a statement.

Moreover, the international organisation also urged nations to not require proof of vaccination against COVID-19 for international travel as the only pathway or condition permitting international travel. It stated that inequitable distribution of COVID-19 vaccines and critical unknowns regarding the efficacy of vaccination in reducing transmission were the reasons behind its stance. It also stated that preferential vaccination of travellers could result in inadequate supplies of vaccines for priority populations considered at high risk.