University of Georgia

Pertussis persists

illustration of lungs infected by pertussis
Pertussis, a respiratory infection caused by the bacterium Bordetella pertussis, was nearly eliminated when vaccination began in the 1940s but has made a comeback since the mid-1970s.

Why has pertussis—more commonly known as whooping cough—experienced a resurgence in the United States? It’s probably not due to an ineffective vaccine, according to a team of UGA researchers, but rather is a predictable consequence of incomplete vaccination coverage.

“This study is important in that it revealed that there has been no change to the epidemiology of pertussis that is causing the rise in the number of cases,” says senior author Pejman Rohani, who has a joint appointment in the College of Veterinary Medicine and the Odum School of Ecology. “Instead, it is a function of the way vaccines were administered over the decades. It is an effect that takes a long time to manifest.”

Pertussis is a respiratory infection caused by the bacterium Bordetella pertussis, which can cause serious infections in infants and young children. Routine vaccination for the disease began in the 1940s and led to a hundredfold decrease in the number of reported cases—to the point that the prospect of eliminating the disease seemed possible. But, since the mid-1970s, pertussis has made a comeback.

Rohani and his team examined long-term surveillance data from Massachusetts to try to understand why.

The most popular theory on the increase of pertussis cases is that the new generation of vaccines is somehow flawed, but Rohani and his colleagues saw no evidence to support this idea. Instead they found that today’s pertussis vaccines, like earlier ones, are largely very effective.

They discovered that high rates of vaccination when the vaccine was first introduced led to an overall decrease in transmission across the population. Due to “herd immunity,” even those who weren’t vaccinated were therefore less likely to contract the disease.

As vaccinated individuals aged, however, the protection afforded by the vaccine began to wear off in some cases. Furthermore, there are fewer and fewer people alive today who survived pertussis infections in the days before vaccination and thus gained lifelong immunity.

This combination means that the number of people who are susceptible to contracting pertussis is slowly rising—setting the stage for an increase in the number of new cases, especially in older individuals.

The results of this study will help to serve as a guide for future vaccination campaigns. The model identifies the core transmission group to be schoolchildren, so the researchers recommend focusing vaccination campaigns on that group, rather than the current emphasis on vaccinating adults. Going forward, researchers will further analyze the results of this study to assess the number and frequency of booster vaccines.

The team’s findings were published in Science Translational Medicine.

The paper’s co-authors include scientists from the University of Michigan, the Institut Pasteur at the University of Versailles St-Quentin-en-Yvelines, and the University of Manitoba.

This story appeared in the fall 2018 issue of  Research Magazine. The original press release is available at