One shot of the Pfizer and Moderna vaccines are not enough to produce protective immunity in kids. You really need to give either three doses of the Pfizer vaccine or two doses of the Moderna vaccine to induce protective immunity against COVID in kids under five. The immune system is kind of like a young developing brain. You need to read something multiple times often to remember it. Your immune system is kind of the same way. Just one dose is not going to do it. Your immune system needs to see it a couple times.
