Many people would balk at the idea of having something inserted into their noses, particularly if that something was infectious whooping cough bacteria. So you’ve got to commend the 34 people in the United Kingdom who bravely volunteered to get live whooping cough bacteria dripped into their noses, for science.
The study, known as a human “challenge model,” intentionally exposed healthy adults to whooping cough bacteria in a safe and controlled lab environment.
The model might one day help scientists develop a better vaccine for whooping cough, also known as pertussis — a disease that’s on the rise in both the United States and in Europe. [27 Devastating Infectious Diseases]
None of the study participants became miserably ill; in fact, most experienced no symptoms at all. And that was the plan: The study aimed to give volunteers a dose of the bacteria that was just enough to allow it to infect them, but not enough to cause symptoms.
“We didn’t want to cause disease,” said lead study author Dr. Hans de Graaf, a researcher at the University Hospital Southampton NHS Foundation Trust. Indeed, if participants were to start looking unwell, they would’ve been given antibiotics to treat the infection right away. “[Although] adults don’t die of pertussis, it’s a really annoying, horrible disease to have,” de Graaf told
De Graaf presented the findings on Oct. 4 at IDWeek, a meeting of several organizations focused on infectious diseases. The findings have not yet been published in a peer-reviewed journal.
Whooping cough, which is caused by the bacterium Bordetella pertussis, is a highly contagious respiratory illness that can be serious, and even deadly for infants. In adults, the illness can lead to coughing fits so violent, they cause people to break ribs.
Although there is a vaccine for whooping cough, cases of the disease have been on the rise in recent years. In 2012, there were nearly 50,000 cases of whooping cough reported in the U.S. — the highest number in more than 50 years. Although the number of cases dropped to around 16,000 in 2017, that’s still higher than in decades past, according to the Centers for Disease Control and Prevention.
Some studies have linked the rise in cases in part to changes made to the whooping cough vaccine formulation, which reduced side effects from the shot, but also appeared to result in waning protection after a few years.
To develop a better whooping cough vaccine, scientists need to know more about people’s immune response to the bacteria, and the type of immune response that results in protection. The researchers aimed to study this by inoculating people directly with the bacteria, and taking blood samples to monitor their immune response.
The study included healthy people ages 18 to 45 who had low levels of antibodies againstB. pertussis, which meant they hadn’t had a recent infection with the bacteria (including an infection that didn’t cause symptoms.) All participants needed to be vaccinated against whooping cough, but not recently — the vaccination had to have taken place at least five years before the study.
After screening 54 volunteers, 34 met the criteria to enter the study. The volunteers were compensated up to $4,600 (3,500 British pounds) for their time and the inconvenience caused by the procedures.
Participants were asked to lie on their backs while the scientists dripped fluid containing the bacteria into each nostril, for about 1 minute per nostril.
Researchers first started with a very low dose of B. pertussis in a few volunteers, and gradually increased the dose as they inoculated more volunteers, until 70 percent of volunteers became “colonized” with the bacteria. This means the bacteria were living in their nose, but the participants didn’t have symptoms.
The participants were then admitted to the hospital research unit for 17 days, where they each had a private room, and access to a recreation area. If participants left their designated area (which was allowed only at certain times), they needed to wear a mask to prevent infection of others.
The majority of participants experienced no symptoms. A few participants experienced mild symptoms including nasal congestion and cough. However, it’s unclear if these symptoms were actually a result of the B. pertussis bacteria, or if some of the participants had allergies, or if they came down with something right before starting the study.
Still, none of these symptoms were serious enough to require the participants to leave the study or get treatment.
Participants also performed tasks to so researchers could see if they were “shedding” the bacteria in their cough or spit. For example, participants were asked to read the tongue twister “Peter Piper picked a peck of pickled peppers” while in a special chamber, called a “coughbox,” in which the air was sampled for bacteria. None of the participants shed the virus in their cough or spit.
At the end of the study, all of the participants received antibiotics to clear the infection.
The next phase of the study will be to examine people’s immune response to B. pertussis in more detail. In the future, researchers could test a vaccine for whooping cough by vaccinating all participants before the study, and seeing if the vaccine protected against colonization, de Graaf said.
Even in the current study, some volunteers did not become colonized by B. pertussis. These participants could help researchers find “biomarkers” for protection against pertussis. “What do these…people have that protects them against colonization, and is that a biomarker of protection we can find,” de Graaf said.
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