Pertussis resurgence: Incomplete coverage and vaccination ‘hesitancy’

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Doctor pediatrician injecting vaccine to cute african girlThe resurgence of whooping cough in the US is a predictable consequence of incomplete coverage, especially among schoolchildren with a highly effective vaccine, research finds. Meanwhile, another study blames the failure to vaccinate not only on bad parenting, but on systemic problems, most importantly, a lack of political will for a national immunisation schedule.

A team of researchers including scientists from the University of Georgia has found that the resurgence of pertussis, more commonly known as whooping cough, in the US is a predictable consequence of incomplete coverage with a highly effective vaccine. This finding goes against pervasive theories on why we are seeing a steady increase in the disease even though the vaccine is given at an early age.

“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,” said senior author Pejman Rohani, who has a joint appointment in the UGA 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 100-fold 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 that. Instead they found that today’s pertussis vaccines, like earlier ones, are largely very effective despite not providing 100% lifelong protection to those individuals who get vaccinated.

What they did discover was that high rates of vaccination when the vaccine was first introduced led to an overall decrease in transmission across the population. Even those who weren’t vaccinated were therefore less likely to contract the disease.

As vaccinated individuals age, however, the protection afforded by the vaccine begins to wear off in some cases. Furthermore, there are fewer and fewer people still alive 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. This is known as the “end of the honeymoon” period.

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 that group should be the main focus of vaccination campaigns, 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.

Besides Rohani, the paper’s co-authors are Matthieu Domenech de Cellès of the University of Michigan and the Institut Pasteur at the University of Versailles St-Quentin-en-Yvelines; Felicia Maria G Magpantay of University of Michigan and University of Manitoba and Aaron A King of the University of Michigan.

Abstract
The resurgence of pertussis over the past decades has resulted in incidence levels not witnessed in the United States since the 1950s. The underlying causes have been the subject of much speculation, with particular attention paid to the shortcomings of the latest generation of vaccines. We formulated transmission models comprising competing hypotheses regarding vaccine failure and challenged them to explain 16 years of highly resolved incidence data from Massachusetts, United States. Our results suggest that the resurgence of pertussis is a predictable consequence of incomplete historical coverage with an imperfect vaccine that confers slowly waning immunity. We found evidence that the vaccine itself is effective at reducing overall transmission, yet that routine vaccination alone would be insufficient for elimination of the disease. Our results indicated that the core transmission group is schoolchildren. Therefore, efforts aimed at curtailing transmission in the population at large, and especially in vulnerable infants, are more likely to succeed if targeted at schoolchildren, rather than adults.

Authors
Matthieu Domenech de Cellès, Felicia M. G. Magpantay, Aaron A. King, Pejman Rohani

 

A legacy of social and political factors rather than bad parenting may be influencing people’s decisions not to vaccinate their children, according to a study from the University of Waterloo.

The study shows that a history of drug scandals, medical training practices, and a lack of political priority placed on disease prevention that started in the 1960s could be responsible for the immunisation apathy, also known as vaccine hesitancy, we’re seeing today.

“It’s not all about the parents, said Heather MacDougall, history professor at Waterloo and co-author of the study. “History reveals systemic problems including lack of public education, lack of access, lack of training, and, perhaps most importantly, lack of political will for a national immunisation schedule.”

MacDougall and co-author Laurence Monnais of Université de Montréal, trace and analyse the contested adoption of the measles vaccine over three decades up to 1998, just before the infamous Andrew Wakefield publication that falsely linked the MMR vaccination to autism.

Their study shows that the vaccine hesitancy phenomenon started well before the 1990s and offers insight on the forces at play behind current instances of vaccine hesitancy. The historians documented trends since the 1960s, such as the thalidomide disaster of 1962, and the emergence of new styles of parenting, second-wave feminism, and the popularisation of alternative medicine.

Measles outbreaks in the 1970s and 1980s corresponded with a shift to individual rather than collective responsibility for personal health and health promotion, according to the study. By the 1990s, the national and international focus on children’s rights and child health made young parents more willing to question whether their child would benefit from vaccination.

“Lack of sustained training in the rapidly changing science of immunology left Canadian health care practitioners with limited knowledge to provide guidance when asked to explain the benefits of vaccination to anxious parents,” said MacDougall.

The division of federal, provincial, and territorial powers over healthcare have created a systemic disadvantage for the consensus needed to develop a consistent national immunisation programme.

“By publishing our research, it confirms the relevance of humanities disciplines such as history to help us understand social phenomena such as vaccine hesitancy in the face disease outbreaks,” said MacDougall.

University of Georgia material
Science Translational Medicine abstract
University of Waterloo material
Canadian Medical Association Journal article (CMA members only)


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