The top US health department plans to require placebo testing for all vaccines in an effort to offer "straightforward" public health information, but experts say such testing could limit availability and raise ethical concerns.

In a shift away from next-generation Covid-19 vaccines, the Trump administration is investing $500 million in a vaccine project championed by two scientists who were recently tapped to serve in senior roles within the National Institutes of Health,

The potential change outlined in a statement would require all new vaccines to undergo placebo testing, sparking concerns among medical experts.