Explaining the resurgence of whooping cough

What is it about?

Whooping cough is caused by a bacteria called Bordetella pertussis, and is a serious and sometimes fatal infection of young infants. For years the disease was well controlled using vaccines made from mixtures of killed B. pertussis germs (so-called 'whole cell (wP) pertussis vaccines). But while these worked very well, they had quite serious side effects. Consequently, in the past 2 decades, the US, UK, and many other countries switched to newer so-called 'acellular' (aP) pertussis vaccines. These are much more tolerable. Unfortunately, it appears that they are also less effective than wP vaccines, because the disease has come back in many of the countries that made the wP to aP switch. The key question is why. Our paper summarizes the science surrounding this question, and reaches the conclusion that traditional explanations for the resurgence have been insufficient. Instead, we conclude that the key issue is that the wP and aP vaccines work in fundamentally different ways in terms of the kinds of immune responses they create. And the key difference is that wP vaccines induced 'mucosal immunity', while the aP vaccines do not. Mucosal immunity is the ability of a person to block or impede a bacteria settling upon and growing on the respiratory tract and therefore being able to cause disease. wP vaccines interfere with mucosal carriage, while aP vaccines do not. The result is that wP vaccines prevent the population more effectively than aP vaccines do, since they make it much harder for B. pertussis to move from person to person, even if those infections do not lead to noticeable symptoms.

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Why is it important?

Our focus on mucosal immunity argues for a pardigm shift in terms of how we study Whooping cough. We argue that it is not sufficient to focus just on patients who have classic symptoms of pertussis (i.e., whooping coughs), but that we also need to know whether patients are asymptomatically infected, and yet still contagious. Since the current aP vaccines are not succeeding in controlling Whooping cough sufficiently, there is interest in creating a third generation of pertussis vaccines. We argue that showing the value of those vaccines will hinge on their ability to demonstrate robust mucosal immunity.

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