If it wasn't for the UK variant virus currently zipping through big sections of the population then I'm sure they would stick with the recommended 2 jabs per person and it is a sign of their desperation that they have gone with a single jab.
They could also be having one eye on the South Africa variant - which is frightening in that it is quite close to making a jump that will let it evade the antibodies generated in response to having been naturally infected or having had one of the vaccines. If that, no it isn't if, it is when that jump happens then they will need to reformulate the vaccine and do everyone all over again.
Nobody is saying this out loud yet, but with the speed of variation shown, we are almost certainly looking at needing new Covid vaccinations every 12 to 18 months.