The study was to be funded with $1.6m from the US Centers for Disease Control and Prevention (CDC), along with another $1.6m from private partners like the Bill Ackman-backed Pershing Square Foundation and the Bluebell Foundation.

“The solution is clear here: take the money and vaccinate as many kids as you can,” said Paul Offit, a vaccines expert at the Children’s Hospital of Philadelphia, who sharply criticized the proposed study as unethical.