Risk less by 4mo
The classic definition of sids
involves all unexplained deaths under a year which enables reserchers a zone to focus on.
However there is a significant fall off in the frequency by the time a child reaches 4mo for reasons that are unclear. Since babies may begin to roll over by 4-5 mo this is comforting.You do not need to strap them down for a year to be safe, just try to start them on their back.