In line with this, a small subgroup of under-fours (n = 4) that were primed with an aP vaccine lacking a Fim2/3 component likewise showed minimal anti Fim2/3 responses after infection, while the under-fours primed in infancy with a Fim2/3 containing aP vaccine (n = 30) showed high anti Fim2/3 responses after infection. Here, CSF1R is linked to infection.