Babies less than six months old do not cough, but they manifest shortness of breath and severely deficient supply of oxygen to the body (asphyxia) and are the most likely to die of the disease unless they receive suitable treatment.
Dojenčki, mlajši od šestih mesecev, ne kašljajo, se pa pri njih kaže oteženo dihanje in resno zmanjšan dovod kisika v telo (asfiksija). Če niso deležni ustreznega zdravljenja, za boleznijo zelo pogosto umrejo.