Whooping cough, also known as the 100-day cough, is caused by a bacterium, Bordetella pertussis. Once nearly vanquished, pertussis is again a significant public health problem in the US. The cough is severe and uncontrollable with a distinct “whoop” sound. For adults it can cause weeks of misery — including rib fractures, fainting, and pneumonia — and for young infants it can be deadly. Worldwide, pertussis causes tens of millions of infections and over a hundred thousand deaths in young children every year. In the US, tens of thousands of cases are reported annually, with periodic epidemic surges.
For decades pertussis was largely controlled in the US thanks to the DTP vaccine, which contained whole pertussis bacteria. DTP often caused high fevers and, rarely, seizures. Some parents believed it caused brain damage, although expert review panels never confirmed a link to permanent neurological injury. Concerns about these side effects — along with lawsuits against manufacturers — led to the development of a safer alternative: the acellular pertussis vaccine (DTaP for children, Tdap for adolescents and adults). These vaccines indeed cause far fewer reactions. However, years after the switch it became clear that immunity from acellular pertussis vaccines wanes faster than immunity from the old whole-cell vaccine. Protection is strongest in the first year after vaccination and declines significantly over the following few years. Researchers are working on improved pertussis vaccines, but for now the current vaccines remain the best available tool for prevention.
When is it especially important to get vaccinated? If you are pregnant, if someone in your family is pregnant, or if you are around young children — especially young infants. The vast majority of pertussis deaths occur in babies under two months of age, before they are old enough to be fully vaccinated. Getting vaccinated during pregnancy helps protect newborns during this vulnerable window.