Children who are vaccinated against pertussis are at lower risk of contracting the disease, but that protection wanes over time, likely contributing to recent outbreaks, researchers found.
A team from Kaiser Permanente Northern California (KPNC) set out to look at effectiveness of diphtheria, tetanus and acellular pertussis (DTaP) vaccine, which is given in five doses beginning at 2 months of age.
Using data on 469,982 children born at KPNC between 1999 and 2016, researchers found 96% were age-appropriately vaccinated. Of 738 with confirmed pertussis, 82% had received all recommended doses of DTaP, according to “Acellular Pertussis Vaccine Effectiveness Over Time,” (Zerbo O, et al. Pediatrics. June 10, 2019, https://doi.org/10.1542/peds.2018-3466).
While there were more pertussis cases among fully vaccinated children than those who were unvaccinated and undervaccinated, these children still had significantly lower risk of pertussis than their peers. The risk was 13 times higher for those who were not vaccinated and twice as high for those who were undervaccinated. Children who received all five doses plus an extra dose were protected even more.
However, as the time since the last dose increased, so did the risk of pertussis. Among vaccinated children ages 19 months to under 7 years, the adjusted risk of pertussis three or more years after vaccination was five times higher than the risk less than a year after vaccination, according to the study.
Among children ages 7-11 years, the adjusted risk of pertussis six or more years after vaccination was twice as high as the risk less than three years after vaccination.
“While the pertussis vaccines don’t last as long as we would like, they do work and they are effective, so both families and providers need to understand it continues to be very important to make sure all infants and children are vaccinated with all doses of the pertussis vaccine and on the recommended schedule,” co-author Nicola P. Klein, M.D., Ph.D., FAAP, director of the Vaccine Study Center at KPNC, said in a video abstract.
In a related commentary, Kathryn Edwards, M.D., FAAP, highlighted the need to improve pertussis vaccines to address waning immunity. She noted experts from around the world are looking into several options, including a live attenuated pertussis vaccine, alone or in combination with DTaP, and adding other antigens or adjuvants to the current vaccines.