Professor Arthur Reingold is Head of Epidemiology at UC Berkeley’s School of Public Health
California: Is whooping cough coming back?
We certainly are having a resurgence of pertussis in the United States, although it’s never gone away. It is a threat to very young infants, particularly those too young to be vaccinated or who have not yet had a complete series of the vaccines.
Where does pertussis come from? How can you catch it?
There is no nonhuman source of pertussis. Pertussis is limited strictly to humans. There are no animals that are involved in the transmission of pertussis and it’s not in the environment. So it’s 100 percent a disease that is transmitted from one person to another through coughing and sneezing, through the respiratory route.
You can be immunized and protected against getting the disease, pertussis, but still have the organism in your nose and throat and spread it to others. Or you can have a very mild illness that is caused by pertussis that causes you to cough, and thereby infect others. So the immunity is not 100 percent from the pertussis vaccine. And what it means is any kind of herd immunity—the way we see, for example, much more powerfully with measles—really can’t be relied upon.
What’s herd immunity?
Herd immunity—the idea that some unvaccinated people are protected because other people are vaccinated and thereby are less likely to come in contact with the organism—is very powerful for some infectious diseases and totally nonexistent and irrelevant for other infectious diseases. Pertussis is kind of in the middle.
Herd immunity is important, and one of the strategies we have for trying to prevent disease in newborn infants who are still too young to be vaccinated is called “cocooning,” where we try to vaccinate all of the adults in the household or who are in contact with that infant. But if people think they’re protected because they live in a generally well-vaccinated population like the United States, and therefore are not likely to get pertussis, that would be the wrong message to give, because the reality is the organism circulates freely in the U.S. despite high levels of vaccination.
In part because we don’t really have another way to protect young babies except to make sure that, A, they are born to well-immunized mothers and have some passive immunity from antibodies they get from their mother. But then it’s going to be several months before they can have had several doses and be protected through immunization, and we know that most babies who get pertussis get it from immediate contact within their family and the adults in their surroundings. So, B, we are trying to at least reduce the likelihood that the adults around a baby could be a source of infection for the baby.
Who doesn’t get vaccinated?
So the Supreme Court basically ruled 100 years ago that you must allow people exemptions on religious, personal-belief kinds of grounds. So that’s sort of been basically adjudicated a long time ago, is my understanding. There are also rare instances where you shouldn’t vaccinate. For example, [if] you’ve had a severe allergic reaction to a vaccine, you shouldn’t get more doses of that vaccine. So there are some medical counterindications—they are very rare—but they do exist. And then the whole question is, other than medical counterindications, … what types of religious or personal-belief exemptions do you allow?
But the easier it is for parents to opt out, the higher the proportion of parents who do opt out, and within states that make it easier, there are higher levels of opting out. Particularly there are pockets in the states of Washington and Oregon and California, including here in Northern California but also in Southern California, where as many as 20 or 30 percent of parents are opting out of vaccinating their children against pertussis. There are pockets here on the West Coast, and I suppose elsewhere, where that’s really reached an alarming proportion.