Whooping cough is a terrible disease in babies
and it is the under-1 year-olds that are the most severely affected with nearly 1% of the infected dying from it.
The incubation period is between 4 – 21 days and during this time it is highly contagious with up to 80% of the unvaccinated catching it.
The main reservoir of infection is in adolescents and young adults (whose personal immunity has worn off). But for all of us (even if we get the native infection) the antibody level (hence our immunity to the disease) wanes over a couple of years.