[amelius]

https://en.wikipedia.org/wiki/Amber_alert

Amber alert means something different than the author thinks ...

[kazinator]

They wanted "red alert".

https://en.wikipedia.org/wiki/Red_Alert

This is just an idiom for denoting a high alert state.

[RupertSalt]

No, "Red Alert" is called when there is an attack imminent, incoming weapons detected, enemies sighted.

So a macrophage on "red alert" would be reacting to an active infection or disease.

[kazinator]

Sure, and this vaccine goads the macrophage into that state, putting it on "red alert", without there actually being an infection.

[RupertSalt]

I suppose it is not worth debating a metaphor written by BBC reporters for the general public, without even reading the research.

But I was edified to learn that Dr Edward Jenner was a vaccine pioneer even without the honors of knighthood.

[resoluteteeth]

Notice that that Wikipedia page links to a disambiguation page which links to https://en.wikipedia.org/wiki/BIKINI_state which may be more familiar to people in the UK than the meaning you are thinking of

[RupertSalt]

Perhaps "Defcon 02" would be better understood?