Rounding up the Herd

As I have discussed in a previous post here, Pertussis, also known as whooping cough, is increasing in prevalence. There are outbreaks this year across the country, building on previous outbreaks last year and in 2010. In order to control these outbreaks, there are a number of strategies being suggested to increase immunization rates—from adding another adolescent dose of the vaccine, to increasing adult vaccination. However, one prominent population that has been a focal point in these outbreaks cannot currently be vaccinated: infants under 6 weeks of age, for whom the vaccine is not approved (pertussis vaccination starts with the routine shots at 2 months of age). How can we protect these infants?

A recent post on’s twitter feed linked to an article about the possible introduction of a newborn pertussis vaccine. This is a wonderful idea and could certainly help to address protection of infants from pertussis. However, either testing either the current DtaP vaccine or developing a newer version for use in this population are time-consuming propositions, both. On the order of years. And that will do nothing for people currently at risk from outbreaks currently in progress. There is another way to protect infants though, one that relies on the concept of herd immunity.

Herd immunity is the idea that by vaccinating a large enough number of individuals in a population–the “herd”–we will effectively halt transmission of the disease because there are not enough potential susceptible hosts. Thus the people who are unable to be vaccinated—infants in this case—will be protected by virtue of being surrounded by immune individuals. In the case of infants, this surround effect is rather evocatively called cocooning, with the idea of blanketing a baby with healthy, vaccinated people. This is accomplished in practice by vaccinating an infant’s mother, father, and caretakers. Previous efforts to accomplish this had relied on vaccinating the mother during pregnancy and encouraging others to be vaccinated during the same time period. But nearly every baby in the US is born in a hospital or similar facility and stays in the nursery for 2–4 days. Could the family be vaccinated then? The answer is a most emphatic yes!

Here in New York State, thanks to brilliant research and lobbying efforts of Shetal Shah, MD, a colleague of mine here at Stony Brook, this practice of cocooning— by encouraging vaccination of caretakers prior to the infant’s discharge home from the hospital—will now be law. Through work published in the journal Pediatrics in 2008, Dr Shah showed that the practice of vaccinating parers and caretakers prior to NICU discharge (Dr. Shah works in the neonatal intensive care unit) was well-tolerated, feasible, and effective. As the rather thorough press release explains, beginning January 2013, all parents and caregivers will be offered and encouraged to accept pertussis vaccination before taking their baby home from the hospital. The hope and aim is this will help to prevent pertussis cases in these infants in the event of an outbreak.

I for one am proud to live in a state so responsive to appropriate medical lobbying efforts, and so proactive in its vaccination practices. The next step is to broadly implement similar cocooning practices across the country and encourage similar laws in state legislatures elsewhere. Let’s get started!