Does the pertussis vaccine reduce the incidence of whooping cough? The answer to that question is not clear.

Part of the problem is that doctors are not well-trained to diagnose pertussis. A prolonged cough may be the only symptom of the disease. And many doctors think whooping cough was eradicated by the pertussis vaccine.

Therefore, they don’t even order a lab test to check for it.

In the 1990s, the World Health Organization (WHO) established a new standard for diagnosing whooping cough. The new standard required laboratory confirmation and 21 days of severe coughing.

Before this time, whooping cough was frequently diagnosed by the characteristic “whoop” associated with a cough.

The new WHO standard would eliminate a substantial number of cases that would have been classified as whooping cough.

The disease is still occurring, but because of changes in the diagnostic criteria, it is not being recognized.