They know the vaccine that's causing it - this isn't new, it's just very rare in a country that predominantly administers the inactivated vaccine. This is just

They know the vaccine that's causing it - this isn't new, it's just very rare in a country that predominantly administers the inactivated vaccine. This is just the result of the joint probability of someone recently being vaccinated with the live attenuated vaccine, being in London (likely traveling there), and the vaccine converting to a more pathogenic type.