my boy starts to have eczema after 5in1 and it cant seems to cure or lessen the red rashes, why is it so? how can i cure it?

Considering that anything which causes an immune response can trigger eczema, so maybe the vaccination did cause the flare up. You can soothe the eczema symptoms by applying aloe vera gel and keeping your child as cool and as comfortable as possible? And to let the skin calm down on its own.