Pertussis vaccination: our gift to others and to the common good
Whooping cough (pertussis) has been in the news for the past several months. For example, there’s been a sizable epidemic in California over the summer that has caused several deaths in infants. I’ve cared for several cases myself recently, including a couple of infants who needed mechanical ventilators to breathe, and who coughed so much for weeks afterward they could barely eat. It’s a serious and potentially lethal infection for infants, although in older children and adults it mainly causes only a nagging cough.
We have a vaccine for pertussis. It’s combined with other vaccines — diphtheria and tetanus — in a single shot, called DTaP. Each capital letter stands for one of the three vaccines in the shot; the little “a” indicates that the pertussis vaccine component is “acellular,” to distinguish it from the older version (the DPT) made from whole pertussis bacteria. That version caused more reactions (mainly high fever) in children who received it than does our current, acellular variety. A child should receive the DTaP at 2, 4, 6, and 18 months, and again at 4-6 years of age.
Overall, pertussis vaccine has been a success, with the number of annual cases, and death rates, dropping enormously. (You can read about its development here.) But the pertussis vaccine has never been a very good one, compared with most of the other ones, such as those for polio or measles.
The ideal vaccine confers life-long immunity. Generally this requires a series of shots to boost immunity, but, once achieved, the person can never get the disease. In practice, all immunity wanes with age and with the passage of time from the last booster shot. This waning is quite pronounced with pertussis vaccine; probably the majority of adults who received their shots as children are no longer immune. They can get pertussis, although when they do their symptoms are just those of a nagging, chronic cough. Even though their symptoms are not severe, they can still infect others — especially infants. And their disease can be life-threatening.
The persons most vulnerable to getting severe or fatal pertussis are infants, often before they can even get their first vaccine shot. So the only way to protect them is for everyone else to be vaccinated so as to be unable to bring the infection to them. Our current vaccine works in older children. And we now have a pertussis booster shot that restores immunity in adolescents and adults. It is called Tdap, and I strongly encourage every adult to get this, especially if you are exposed to young children.
Pertussis vaccine is unusual in this way. All vaccine strategies for protecting populations involve what is called herd immunity, but the principle for controlling pertussis is primarily based upon keeping those for whom the disease is only mild vaccinated, so that they may be prevented from passing the infection to infants who are too young to join the vaccinated herd. We do it for the common good.
You can find an enormous amount of useful and reliable information here, at the Vaccination Education Center maintained by the Children’s Hospital of Philadelphia.