During the severe coughing stage, seizures or even death can occur, particularly in an infant. Immunized school children and adults have milder symptoms than young children. Potential Complications Pertussis is most dangerous to children less than 1 year old. Complications for infants include pneumonia, convulsions, and in rare cases brain damage or death. Serious complications are less likely in older children and adults.
Pertussis is spread through respiratory droplets when an infected person coughs, sneezes or talks.
The greatest risk of spread is during the early stage when it appears to be a cold. Those treated with antibiotics are contagious until the first 5 days of appropriate antibiotic treatment have been completed. Anyone who is exposed can get pertussis. Unimmunized or inadequately immunized people are at higher risk for severe disease. Many cases occur in adults because protection from the vaccine lasts only 5 to 10 years after the last dose.