From the Journals

Waning pertussis immunity may be linked to acellular vaccine

View on the News

How can we address waning immunity of acellular pertussis vaccine?

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.



large Kaiser Permanente study paints a nuanced picture of the acellular pertussis vaccine, with more cases occurring in fully vaccinated children, but the highest risk of disease occurring among the under- and unvaccinated.

Small child receiving a vaccine Sean Locke/iStockphoto

Among nearly half a million children, the unvaccinated were 13 times more likely to develop pertussis than fully vaccinated children, Ousseny Zerbo, PhD, of Kaiser Permanente Northern California in Oakland and colleagues wrote in Pediatrics. But 82% of cases occurred in fully vaccinated children and just 5% in undervaccinated children – and rates increased in both groups the farther they were in time from the last vaccination.

“Within our study population, greater than 80% of pertussis cases occurred among age-appropriately vaccinated children,” the team wrote. “Children who were further away from their last DTaP dose were at increased risk of pertussis, even after controlling for undervaccination. Our results suggest that, in this population, possibly in conjunction with other factors not addressed in this study, suboptimal vaccine efficacy and waning [immunity] played a major role in recent pertussis epidemics.”

The results are consistent with several prior studies, including one finding that the odds of the disease increased by 33% for every additional year after the third or fifth DTaP dose (Pediatrics. 2015;135[2]:331-43).

The current study comprised 469,982 children aged between 3 months and 11 years, who were followed for a mean of 4.6 years. Over the entire study period, there were 738 lab-confirmed pertussis cases. Most of these (515; 70%) occurred in fully vaccinated children. Another 99 (13%) occurred in unvaccinated children, 36 (5%) in undervaccinated children, and 88 (12%) in fully vaccinated plus one dose.

In a multivariate analysis, the risk of pertussis was 13 times higher among the unvaccinated (adjusted hazard ratio, 13) and almost 2 times higher among the undervaccinated (aHR, 1.9), compared with fully vaccinated children. Those who had been fully vaccinated and received a booster had the lowest risk, about half that of fully vaccinated children (aHR, 0.48).

Risk varied according to age, but also was significantly higher among unvaccinated children at each time point. Risk ranged from 4 times higher among those aged 3-5 months to 23 times higher among those aged 19-84 months. Undervaccinated children aged 5-7 months and 19-84 months also were at significantly increased risk for pertussis, compared with fully vaccinated children. Children who were fully vaccinated plus one dose had a significantly reduced risk at 7-19 months and at 19-84 months, compared with the fully vaccinated reference group.

“Across all follow-up and all age groups, VE [vaccine effectiveness] was 86% ... for undervaccinated children, compared with unvaccinated children,” Dr. Zerbo and associates wrote. “VE was even higher for fully vaccinated children [93%] and for those who were fully vaccinated plus one dose [96%].”

But VE waned as time progressed farther from the last DTaP dose. The multivariate model found more than a 100% increased risk for those whose last DTaP was at least 3 years past, compared with less than 1 year past (aHR, 2.58).

The model also found time-bound risk increases among fully vaccinated children, with a more than 300% increased risk among those at least 6 years out from the last DTaP dose, compared with 3 years out (aHR, 4.66).

The results indicate that other factors besides adherence to the recommended vaccine schedule may be at work in recent pertussis outbreaks.

“Although waning immunity is clearly an important factor driving pertussis epidemics in recent years, other factors that we did not evaluate in this study might also contribute to pertussis epidemics individually or in synergy,” Dr. Zerbo and associates wrote. “Results from studies in baboons suggest that the acellular pertussis vaccines are unable to prevent colonization, carriage, and transmission. If this is also true for humans, this could contribute to pertussis epidemics. The causes of recent pertussis epidemics are complex, and we were only able to address some aspects in our study.”

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.

SOURCE: Zerbo O et al. Pediatrics. 2019 Jun 10. doi: 10.1542/peds.2018-3466.

Next Article: