Key clinical point: The acellular pertussis vaccine does not confer persistent immunity.
Major finding: About 82% of the children who developed pertussis were fully vaccinated, even though the unvaccinated faced a 1,200% higher relative risk of the disease.
Study details: The retrospective cohort study comprised almost half a million children followed for nearly 5 years.
Disclosures: The study was funded by Kaiser Permanente Northern California, the National Institutes of Health, and in part by a National Institute of Allergy and Infectious Diseases grant. One coauthor reported receiving research grant support from Sanofi Pasteur, Novartis, GlaxoSmithKline, Merck, MedImmune, Pfizer, and Dynavax for unrelated studies; the other authors reported no relevant financial disclosures.
Zerbo O et al. Pediatrics. 2019 Jun 10. doi: 10.1542/peds.2018-3466.
Fixing one problem with the pertussis vaccine seemed to have created another, Kathryn M. Edwards, MD, wrote in an accompanying editorial.
The current acellular vaccine was approved in 1997. It was considered a less reactive substitute for the previous whole-cell vaccine, which was associated with injection site pain, swelling, fever, and febrile seizures, Dr. Edwards wrote. “For about a decade, all seemed to be going well with pertussis control. Serological methods were employed to diagnose pertussis infections in adolescents and adults, and polymerase chain reaction methods were devised to more accurately detect pertussis organisms. Thus, the burden of pertussis disease was increasingly appreciated as the diagnostic methods improved.”
But things soon changed. There were pertussis outbreaks, some of them quite large. The increasing disease rates showed that protection conferred by the acellular vaccine waned much more quickly than that conferred by the whole-cell vaccine. “In the current study, Zerbo et al. add to the body of evidence documenting the increase in pertussis risk with time after DTaP vaccination,” she noted.
This has several practical implications, Dr. Edwards wrote.
“First, given the markedly increased risk of pertussis in unvaccinated and undervaccinated children, universal DTaP vaccination should be strongly recommended. Second, the addition of maternal Tdap vaccination administered during pregnancy has been shown to significantly reduce infant disease before primary immunization and should remain the standard,” Dr. Edwards wrote.
More problematic is how to address the waning DTaP immunity now seen. “One option presented [at an international meeting] was a live-attenuated pertussis vaccine administered intranasally that would stimulate local immune responses and prevent colonization with pertussis organisms. This vaccine is currently being studied in adults and might provide a solution for waning immunity seen with DTaP vaccine,” she noted.
Another possibility is adding the live vaccine to the current DTaP, which should, in theory, stimulate more long-lasting immunity. But numerous safety studies in young children would be necessary before adopting such an approach, Dr. Edwards wrote.
Adding more antigens to the acellular vaccine also might work, and investigational vaccines like this are in development.
Studies in animals and humans show that acellular vaccines “generate functionally different T-cell responses than those seen after whole-cell vaccines, with the whole cell vaccines generating more protective T-cell responses. Studies are ongoing to determine if adjuvants can be added to acellular vaccines to modify their T-cell responses to a more protective immune response or whether the T-cell response remains fixed once primed with DTaP vaccine,” she wrote.
Dr. Edwards is a pediatric infectious disease specialist at Vanderbilt University, Nashville, Tenn. She wrote an editorial to accompany Zerbo et al (Pediatrics. 2019. doi: 10.1542/peds.2019-1276). She reported no financial disclosures, and received no funding to write the editorial.