doubling every day. reporter: still unclear, if it partially evades vaccines but the other thing that s becoming clearer is that people who were infected with other versions of the sars-cov-2 virus can be reinfected with this one. reporter: new travel restrictions kick in 12:01 a.m. monday. everyone coming in into the u.s. will have to test negative within 24 hours of departure. some experts also advocating domestic travel restrictions. when you go through security, you show your vaccine. uh, card. if you don t if you haven t been vaccinated, you can t get onboard an aircraft. reporter: the biden administration has said it will not do that. the measures that i announced yesterday are we believe are sufficient. but we do require for travel, we are going to continue to require people to have mask on. reporter: the dmijz is now