mRNA vaccines were heralded as a medical marvel that saved lives during the Covid pandemic, but now the US is pulling back from researching them.
US Health Secretary Robert F Kennedy Jr has cancelled 22 projects - worth $500m (£376m) in funding – for tackling infections such as Covid and flu.
So does Kennedy - probably the country's most famous vaccine sceptic – have a point, or is he making a monumental miscalculation?
Prof Adam Finn, vaccine researcher at the University of Bristol, says "it's a bit of both" but ditching mRNA technology is "stupid" and potentially a "catastrophic error".
Let's unpick why.
Kennedy says he has reviewed the science on mRNA vaccines, concluding that the "data show these vaccines fail to protect effectively against upper respiratory infections like COVID and flu".
Instead, he says, he would shift funding to "safer, broader vaccine platforms that remain effective even as viruses mutate".
So are mRNA vaccines safe? Are they effective? Would other vaccine technologies be better?
And another question is where should mRNA vaccines fit into the pantheon of other vaccine technologies - because there are many:
Each has advantages and disadvantages, but Prof Finn argues we "overhyped" mRNA vaccines during the pandemic to the exclusion of other approaches, and now there is a process of adjusting.
"But to swing the pendulum so far that mRNA is useless and has no value and should not be developed or understood better is equally stupid, it did do remarkable things," he says.

