For children who have either experienced a delay in pertussis vaccination or who haven’t received the recommended number of doses, what is their risk of pertussis? A new study provides answers.
With the pandemic raging for nearly a year and a half, many children have missed routine childhood vaccinations. What is the risk of pertussis in infants and young children who are either undervaccinated or have experienced a delay in their diphtheria-tetanus–acellular pertussis vaccine, which is administered as a 3-dose series in infancy with a booster at age 5 years?1
The population-based, retrospective cohort study utilized Washington State Immunization Information System data and pertussis surveillance data from Public Health Seattle and King County, Washington. It included participants who were aged 3 months to 9 years and were born or living in King County, Washington, between January 2008 and December 2017. Being undervaccinated was described as receiving fewer doses than recommended at a given age. Delayed vaccination was defined as not being administered the vaccine doses in the time frames recommended by the Centers for Disease Control and Prevention.
There were a total of 316,404 children, representing 17.4 million person-months of follow-up included in the study. No vaccines were recorded in the Immunization Information System for 19,943 (6.3%) of children. A delay in vaccine was noted for 116,193 children (36.7%) and 180,268 (56.9%) were fully vaccinated without a delay. Both undervaccination and delayed vaccination were higher for older children (17.6% delayed or undervaccinated at age 2 months for dose 1 at 3 months vs 41.6% at age 5 years for dose 5), but this rate improved within successive birth cohorts (52.2% for 2008 birth cohort vs 32.3% for 2017 birth cohort). The investigators found that undervaccination was significantly linked to a higher risk of pertussis (adjusted relative risk [aRR], 4.8; 95% CI, 3.1-7.6), the first booster (aRR, 3.2; 95% CI, 2.3-4.5), and the second booster (aRR, 4.6; 95% CI, 2.6-8.2). A delay in vaccination among children who did end up receiving the recommended number of doses was not tied to a risk of pertussis.
According to the investigators, undervaccination was tied to a higher risk of pertussis. However, short delays in vaccination appear to be less important than previously thought, as long as the child received the age-appropriate number of doses, although delays are not recommended. For clinicians facing a number of undervaccinated or delayed vaccines in their patients, the key takeaway is that ensuring all doses of pertussis are administered is imperative.