If a Covid-19 vaccine is proven effective, the US will ensure it's distributed for free to all Americans, officials said Thursday, underscoring there will be no shortcuts on safety. "We are not at all reducing the regulatory rigor with which we will evaluate and hopefully approve vaccines," Paul Mango, a senior health department official, told reporters. Washington has invested more than $10 billion in six vaccine projects and signed contracts guaranteeing the delivery of hundreds of millions of doses should they be approved following clinical trials. Russia this week approved a vaccine even before the start of the last phase of clinical trials, in which the drug is injected into tens of thousands of volunteers to verify its effectiveness and safety. Francis Collins, director of the National Institutes of Health (NIH), compared Russia's vaccineto a game of "Russian roulette."