Nav: Home

Decades-long trends, not flawed vaccine, explain resurgent whooping cough

March 28, 2018

ANN ARBOR--Researchers and public health officials have struggled to explain the resurgence of whooping cough in the United States since the late 1970s, and the suspected shortcomings of the current generation of vaccines are often blamed.

But a new University of Michigan-led study concludes that the resurgence of the highly contagious respiratory disease is the result of factors--including a phenomenon known as the honeymoon period--that began in the middle of the last century, long before the latest vaccines were introduced in the late 1990s.

"Conventional wisdom is that the current vaccine is the problem, but that's not consistent with what we see," said Aaron King, a U-M infectious disease ecologist and applied mathematician.

King and colleagues from the Institut Pasteur, the University of Georgia and Queens University concluded that natural population turnover, incomplete vaccination coverage, and slowly waning protection from a highly effective yet imperfect vaccine best explain the resurgence of whooping cough. The disease can be fatal to infants and is also known as pertussis.

"This resurgence is the predictable consequence of rolling out a vaccine that isn't quite perfect and not hitting everybody in the population with that vaccine," said King, a professor in the U-M Department of Ecology and Evolutionary Biology and in the mathematics department.

The team's findings are scheduled for publication March 28 in Science Translational Medicine. The first author of the paper is Matthieu Domenech de Celle?s, formerly a U-M postdoctoral researcher under King, now at the Institut Pasteur in Paris.

"Our results are important because they show that recent trends in pertussis are not necessarily caused by recent changes in epidemiology or biology," said Domenech de Celle?s.

"Rather, the contemporary epidemiology of pertussis may be interpreted as a legacy of longstanding immunization practices. It's an important shift of perspective, which makes pertussis a complex but exciting system to study."

The researchers used disease-transmission models and 16 years of age-stratified pertussis incidence data from Massachusetts, along with statistical methods for extracting information from the data. The authors say their results apply to the rest of the United States and to Western Europe.

According to the study, the introduction of the first pertussis vaccine in the late 1940s led to a honeymoon period, a time of very low disease incidence following the start of a vaccination program. The return of pertussis in recent decades signals the end of that honeymoon period, according to the researchers.

In the pre-vaccine era, whooping cough was a very common childhood disease in the United States. Most kids were exposed to Bordetella pertussis, the bacterium that causes it, and their immune systems mounted a strong response that provided long-lasting immunity. As a result of those naturally acquired infections, most adult Americans were immune to pertussis.

Routine vaccination with a whole-cell pertussis vaccine quickly led to a 100-fold reduction in incidence. Actually, two factors accounted for that sharp drop-off: children protected by the new vaccine and adults with natural immunity acquired in the pre-vaccine era.

But as the decades passed, the number of American adults with naturally acquired pertussis immunity gradually declined as that older group died out.

Concurrently, the number of pertussis-susceptible U.S. adults was on the rise, setting the stage for the resurgence. The susceptible adults included people who were not vaccinated as children and who also avoided naturally acquired pertussis infections.

The mathematical model that best fit the 1990-2005 Massachusetts incidence data was one that explains the current resurgence "as a legacy of incomplete vaccination with effective, but imperfect, vaccines against a background of slow demographic turnover, i.e., as an end-of-honeymoon effect," the authors wrote.

The modeling study also supports the idea that protection from the pertussis vaccine gradually wanes over time--though it lasts a lot longer than many experts believed.

Some critics of the current acellular pertussis vaccine say it wears off after five to seven years. But the new study "suggests that current pertussis vaccines provide lifelong protection to 55 percent of people and protect 90 percent of people for more than a decade," said study co-author Pejman Rohani, a population ecologist at the University of Georgia's Odum School of Ecology. "Furthermore, our models explain that patterns of pertussis incidence previously attributed to rapid vaccine waning are actually consistent with higher contact rates once children enter school."

Though the current vaccine is effective at reducing levels of the pertussis pathogen circulating in the population, routine vaccination alone will never be sufficient to eradicate the bacterium, the researchers conclude.

In infants, pertussis causes violent, gasping coughing spells and can lead to life-threatening complications. People with whooping cough usually spread the disease by coughing or sneezing while in close contact with others. Parents, older siblings or other caregivers can give whooping cough to babies without even knowing they have the disease.

The modeling study identified primary school children and teenagers as the "core transmission group" mainly responsible for spreading the disease. In one simulation, a booster vaccination effort focused on children ages 5 to 10 or 10 to 20 led to a drop in infant cases of about 25 percent.

"The overwhelming amount of transmission is happening in those age groups," King said. "So, we have to make sure that kids are getting vaccinated before they go to school. That's going to have the biggest impact."

The U.S. Centers for Disease Control and Prevention recommends a series of five pertussis shots for children under 7. Additional shots are recommended for older children and for some adults.

Pertussis is responsible for 195,000 infant deaths each year worldwide, mostly in the developing world. There were 17,972 reported pertussis cases in the United States in 2016, including six infant deaths, according to the CDC.
-end-
The other author of the Science Translational Medicine paper, in addition to Domenech de Celle?s, King and Rohani, is Felicia M.G. Magpantay, formerly a U-M postdoctoral researcher and now at Queen's University in Kingston, Ontario.

The new study is the latest result of efforts funded by a $1.7 million, five-year National Institutes of Health grant to King and Rohani aimed at understanding the causes of pertussis resurgence.

University of Michigan

Related Vaccines Articles:

Understanding T cell activation could lead to new vaccines
Scientists could be one step closer to developing vaccines against viruses such as Zika, West Nile or HIV, according to Penn State College of Medicine researchers.
Vaccines do work for pandemic flu, says study
Vaccines are successful in preventing pandemic flu and reducing the number of patients hospitalized as a result of the illness, a study led by academics at the University of Nottingham has found.
Research could lead to better vaccines and new antivirals
Scientists at Sanford Burnham Prebys Medical Discovery Institute (SBP) have identified a new regulator of the innate immune response -- the immediate, natural immune response to foreign invaders.
Toward opioid vaccines that can help prevent overdose fatalities
In 2014, the number of deaths from opioid overdoses in the US jumped to its highest level on record.
New, more effective strategy for producing flu vaccines
A team of researchers led by Yoshihiro Kawaoka, professor of pathobiological sciences at the University of Wisconsin-Madison School of Veterinary Medicine, has developed technology that could improve the production of vaccines that protect people from influenza B.
A method for storing vaccines at room temperature
Several simple and inexpensive techniques make it possible to store antiviral-vaccines at room temperature for several months.
Engineers design programmable RNA vaccines
MIT engineers have designed programmable RNA vaccines that could be rapidly manufactured and deployed.
Zika vaccines protect mice from infection
A single dose of either of two experimental Zika vaccines fully protected mice challenged with Zika virus four or eight weeks after receiving the inoculations.
Can we hypercharge vaccines?
Researchers at Boston Children's Hospital report that a fatty chemical naturally found in damaged tissues can induce an unexpected kind of immune response, causing immune cells to go into a 'hyperactive' state that is highly effective at rallying infection-fighting T-cells.
Vaccines: Don't leave home without them
While Americans should be fully vaccinated before travelling internationally to avoid infection with highly contagious diseases such as measles and hepatitis A, many are not, suggest two studies being presented at IDWeek 2015™.

Related Vaccines Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#514 Arctic Energy (Rebroadcast)
This week we're looking at how alternative energy works in the arctic. We speak to Louie Azzolini and Linda Todd from the Arctic Energy Alliance, a non-profit helping communities reduce their energy usage and transition to more affordable and sustainable forms of energy. And the lessons they're learning along the way can help those of us further south.