The yellow line refers to the MMR vaccine.

Today, we hear for the quarter and year ending 31 March 2020:

Uptake rates remained high in Scotland; over 96% of children had received each routine immunisation by the time they were 12 months old, apart from the rotavirus vaccine, which had 94.2% uptake.

The above composite graphs from September 2019 remind us of the ongoing risk of viral infection spreading across the border into Scotland, especially measles.

It is not xenophobic only sensible to have border checks.