A travel bubble between Hong Kong and Singapore will begin on Nov. 22, the two cities said on Wednesday, as they moved to re-establish overseas travel links and lift the hurdle of quarantine for visiting foreigners. No quarantine will be required and there will be no restrictions on the reasons for travel. California and several states across the U.S. Midwest tightened restrictions on residents on Tuesday as the nation's top infectious disease specialist called on Americans to remain vigilant until a vaccine can be approved and distributed.