By Nikhila Natarajan New York, April 2 : Social distancing guidelines will likely stay in place in the US until there are "no new cases and no deaths", the White House coronavirus task force has indicated while confirmed COVID-19 cases in the country climbed beyond 200,000 and deaths topped 4,700. "The ultimate solution to a virus that might keep coming back is a vaccine", America's top infectious diseases doctor Anthony Fauci said at a White House briefing on Wednesday. The US now has the world's highest caseload from the pandemic, the wail of ambulances loudest in New York which is reporting the most crushing numbers. Trump is bracing the nation for "horrific" days ahead. Fauci said that by the time the US is ready to relax social distancing guidelines, testing capacity would have to be available at scale. "The one thing we hopefully will have in place is a much more robust system of identifying someone who is infected, isolate them and then do contact tracing", Dr. Fauci said. "A really good program of containment", Fauci said, will give the US enough flex to "never have to get into mitigation". "We are in mitigation right now", Fauci said, referring to the social distancing guidelines that are in place till April 30. Speaking about vaccine development, Fauci said the work is "on target". "We're still in Phase 1, there were three doses, we're in the highest dose now. A few months from now, we'll be in Phase 2", Fauci said. Fauci has stuck firmly to his timeline of "a year or year and a half" for vaccine breakthrough. On antibody testing, Fauci confirmed that "there is a lot of activity centred around a passive transfer of antibodies of convalescent plasma" but clarified that this is not the first priority right now. Testing, he said, is the most urgent task before the US. "It is very important to get a feel for the penetrance of infection in society. You get a better feel for what the herd immunity would be", Fauci explained. This week, the Trump administration revealed for the first time multiple predictive models that are being used to estimate its grim assessment of a 100,000-200,000 coronavirus death toll in the country and stressed that community adherence to social distancing guidelines will be the game changer that will flatten the curve. "There's no magic bullet. There's no magic vaccine or therapy. It's just behaviours. Each of our behaviours, translating into something that changes the course of this viral pandemic over the next 30 days", Dr Deborah Birx, White House coronavirus response co-ordinator, said. "Americans should be prepared for that (death toll). Yes, it is a projection but that's what it is and we have to be prepared for that", said Fauci. The 100,000-200,000 death toll projection "assumes full mitigation measures" currently in place. The current guidelines stop short of a complete lockdown, still allowing people to go outside the home for solitary activities and for essential tasks. "We trust the American people to keep that six feet distance when they go out, meet people. That is why we have not issued a complete lockdown", Birx said. She said that if people maintain "that six feet distance", they have "controlled" the virus. (Nikhila Natarajan can be contacted at @byniknat) /IANS