Children ages 8 to 11 are at high risk of getting whooping cough if exposed — even if they’ve been fully vaccinated. Yep, you read that right. Of course tweens who haven’t had all their DTaP vaccines are more likely than vaccinated children to get the illness if exposed, but research is now showing that only about a quarter of fully vaccinated 8 to 11 year olds retain full immunity.
This waning immunity partially explains the near epidemic outbreaks in California and Michigan a couple of years ago and recently in Washington State. Because even fully vaccinated tweens are susceptible to infection in large numbers, the illness will spread more quickly and widely. It is also true that vaccinated children tend to have milder illness and may not be diagnosed early in the illness allowing them to spread it to more people. In addition, the large number of children with incomplete vaccination makes for an even more serious outbreak.
Why immunity wanes so quickly in children who received five previous DTaP vaccines, the last of which is given at 4 to 5 years of age, is unclear, but I suspect it has to do with the change in the formulation of the vaccine that decreased the side effect profile. The change was made in the mid 1990s and yet it wasn’t until the vaccine rates fell significantly that large outbreaks were seen. It is a combination of the two. Had vaccine rates remained high, the disease would still have found a larger barrier to spreading but once the rates fell the gaping holes in the armor of the vaccinated children were visible.
Children who have been coughing for more than a couple of weeks, who seem perfectly fine unless they are coughing, are suspect for having whooping cough and vaccinated or not, should be tested.
Infants are still at greatest risk for contracting the illness if exposed given that all infants are only partially vaccinated at best and older children or adult caregivers can have pertussis and not get proper diagnosis or treatment. Young infants are also at greatest risk for complications and death from the illness.
Even though vaccination doesn’t work 100 percent, it works very well for the few years just after vaccination for most and immunity wanes three or more years later if at all. Vaccination is still the best choice for young infants, older children, and adult caregivers. Even though it is imperfect, it is our best defense against illlness on a small scale and a large one.