Sitting in the shadow of the brutalist health department building in Washington, with only a leather jacket for protection against an autumnal breeze, Moncef Slaoui cuts a defiant figure. Six months after the former GlaxoSmithKline executive left the private sector to become President Donald Trump’s coronavirus vaccine tsar, Mr Slaoui feels his decision has been vindicated, and critics of the ability of Operation Warp Speed to develop a vaccine in record time having been proved wrong.

“The easy answer for experts was to say it was impossible and find reasons why the operation would never work,” he told the Financial Times. But the vaccine push is now hailed as the bright spot in the Trump administration’s Covid-19 response, as products from Pfizer and BioNTech, Moderna, and AstraZeneca and Oxford university move closer to approval.

Operation Warp Speed is a more than $10bn investment programme with a remit to fund vaccines, therapeutics — such as two recently approved antibody treatments — and diagnostics. So far it has spent the vast majority of its money on Covid-19 vaccines.

As well as funding some vaccine Scientists had warned that, with much still to learn about Covid-19, a vaccine might take longer to develop, manufacture and distribute than Mr Slaoui — and his boss, the president — might have hoped.Mr Slaoui’s team also helped manufacturers secure supplies and sped up responses to usually laborious regulatory queries.

The central achievement of Operation Warp Speed had been accelerating investment in manufacturing, said Angela Rasmussen, a virologist at the Columbia University School of Public Health. “Normally, that would be a huge investment for a vaccine manufacturer to make, and potentially be a huge loss for them if they developed a vaccine that never went on to the market,” she said.

Even Pfizer, which did not take direct investment from Operation Warp Speed, benefited from having a $2bn pre-order.