Adults and older children usually have milder symptoms than young children. How bad your symptoms are also depends on whether you've had the vaccine and how long ago it was. Symptoms of whooping cough usually last 6 to 10 weeks, but they may last longer.dults and older children may not follow this pattern of symptoms. In stage 1, symptoms are like those of a cold: 1  You sneeze and have a runny nose, a mild cough, watery eyes, and sometimes a mild fever. 2  The symptoms last from several days to 2 weeks. 3  This is when you are most likely to spread the disease.