There has been an increase in the numbers of reported cases of B. pertussis (whooping cough) in the United States in recent decades, especially in the past few years. Reported outbreaks of the highly contagious disease have commonly been attributed to waning protection of the pertussis vaccine and low vaccine coverage.
Additionally, researchers have been arguing about whether the B. pertussis organism started evolving shortly after the whole cell DPT vaccine was given on a mass basis to children in the late 1940s followed by introduction of less reactive acellular DTaP vaccine in the mid 1990s. However, now there is wider recognition of scientific evidence that data in recent years points to a fourth cause—asymptomatic transmission of whooping cough by vaccinated individuals.
Reported Whooping Cough Cases Increasing for Decades
In 1922, there were 107,473 reported cases of pertussis in the United States and 5,099 deaths. Pertussis-related mortality declined during the 1940s largely due to improved sanitation, hygiene and access to health care. Although there was a general decline in reported pertussis cases after the DPT vaccine was introduced in the late 1940s, reported cases began to increase in the 1980s.3 One 1977 study published by the U.S. Centers for Disease Control and Prevention (CDC) found whole cell DPT vaccine effectiveness was only 63 percent.
There were 1,010 reported cases of pertussis in the U.S. in 1976 and 25,827 cases in 2004, for a nationwide incidence of 8.5 pertussis cases per 100,000 individuals.5 However, by 2012, there were approximately 48,277 cases of pertussis reported in the U.S.