I used to work with vaccine injuries. They are rare. And usually not very severe. HOWEVER, they were far less common when children got one or two at a time. Once they went beyond just 3 things at once, like the MMR, vaccine injuries did increase. So I would say the research is pretty clear. Kids shouldn’t get multiple vaccines all at once. When Pro Quad was introduced and then given together with other vaccines at the same time—vaccine injuries increased. It’s not a huge increase. But it was an increase.