Some infants, especially those with CMPA, may experience temporary digestive sensitivities or blood in their stool following routine vaccinations. This is often a transient reaction and typically subsides within a day or two. If you notice this, keep a close watch on your baby, maintain their usual diet, and avoid any new allergens. However, always inform your pediatrician to ensure the symptoms are indeed related to the vaccine and not an underlying issue requiring medical intervention.