Advice after MenB vaccine

[Firebug62]

Has anyone ever seen anything like this red line before? Baby had 16 week vaccines yesterday and just noticed this on her thigh, she had the MenB one in this leg. I can't find anything online.
Looks like it's under the skin, no major swelling and baby seems fine in herself, not sure whether to call 111 or wait until morning and see if it's better?

I wonder if it could be a slight allergic reaction to the vaccine. I think it would be no harm to ring 111 to be on the safe side, especially as this isn't a side effect parents are warned about.