Maternal pertussis immunisation: clinical gains and epidemiological legacy

Maternal pertussis immunization and the blunting of routine vaccine effectiveness: a meta-analysis and modeling study

A key goal of pertussis control is to protect infants too young to be vaccinated, the age group most vulnerable to this highly contagious respiratory infection. In the last decade, maternal immunization has been deployed in many countries, successfully reducing pertussis in this age group. Because of immunological blunting, however, this strategy may erode the effectiveness of primary vaccination at later ages. Here, we systematically reviewed the literature on the relative risk (RR) of pertussis after primary immunization of infants born to vaccinated vs. unvaccinated mothers. The four studies identified had ≤6 years of follow-up and large statistical uncertainty (meta-analysis weighted mean RR: 0.71, 95% CI: 0.38-1.32). To interpret this evidence, we designed a new mathematical model with explicit blunting mechanisms and evaluated maternal immunization's short- and long-term impact on pertussis transmission dynamics. We show that transient dynamics can mask blunting for at least a decade after rolling out maternal immunization. Hence, the current epidemiological evidence may be insufficient to rule out modest reductions in the effectiveness of primary vaccination. Irrespective of this potential collateral cost, we predict that maternal immunization will remain effective at protecting unvaccinated newborns, supporting current public health recommendations.

Safety of Maternal Immunization Against Pertussis: A Systematic Review

The WHO recommends vaccination of all children against pertussis. However, newborn infants remain vulnerable to infection. Pertussis vaccination during pregnancy has been introduced in several countries to protect newborns via transplacental transfer of maternal pertussis antibodies to the infant. We reviewed the impact of maternal pertussis vaccination on the health of pregnant women, the developing fetus, and health of the newborn. We searched PubMed/MEDLINE, EMBASE, Scopus (Elsevier), Cochrane Database of Systematic Reviews, ProQuest, and Science Direct to identify studies that assessed the safety of maternal pertussis vaccination. Twenty-seven English language publications published between January 1995 and December 2018 were included in this review. Pregnant women receiving pertussis vaccines did not have increased rates of systemic or local reactions. There were no safety concerns with repeat vaccination with other tetanus-containing vaccines or their concomitant administration with influenza vaccines. Maternal pertussis vaccination did not adversely affect pregnancy, birth or neonatal outcomes. This review confirms the safety of maternal pertussis vaccination during pregnancy. FUNDING: Sanofi Pasteur. Plain language summary available for this article.

Impact of maternally derived pertussis antibody titers on infant whole-cell pertussis vaccine response in a low income setting

BACKGROUND

Maternal vaccines against pertussis are not yet recommended in the developing world. Besides unclear burden estimates, another concern is that transplacental transfer of maternal pertussis antibodies could result in attenuation of the immune response to whole cell pertussis (DTwP) primary vaccination series in infants. This study was taken up to determine whether higher levels of maternal pertussis antibodies attenuate immune response of infants to DTwP vaccination series given at 6-10-14 weeks of age.

METHODOLOGY

A total of 261 pregnant women and their infants from four low-income settlements in Karachi, Pakistan were enrolled in this study. The study endpoints were infant antibody titers for Pertussis toxin (PTx), Filamentous hemagglutinin antigen (FHA), Pertactin (PRN) and Fimbriae type 2/3 (FIM) - from birth through 18 weeks of age. Cord blood or pre-vaccine pertussis antibody titers indicate the concentration of maternal antibodies transferred to infants. Linear regression models were used to determine the association between higher maternal antibody titers and infant immune response to DTwP vaccine. Geometric Mean Ratio (GMR) was calculated as the ratio of infant antibody titers at specified time points against the maternal antibody titers at the time of delivery.

RESULTS

At eighteen weeks of age, the adjusted β regression coefficient for PTx was 0.06 (95% CI: -0.49-0.61), FHA 0.02 (95% CI: -0.26 -0.29), PRN 0.02 (95%CI -0.38- 0.43), and FIM 0.17 (95%CI: -0.21-0.54). Among infants who received at least two doses of DTwP vaccine, higher maternal antibody titers did not have any attenuating effect on infant post-immunization antibody titers against all four pertussis antigens.

CONCLUSION

Maternal pertussis antibodies did not attenuate infant's immune response to pertussis antigens in DTwP primary vaccine given at 6-10-14 weeks of age.

Pertussis manifesting as recurrent cough and wheezing in an incompletely vaccinated 8-month-old infant

Pertussis is an acute respiratory illness caused by Bordetella pertussis, showing a re-emergence in developed countries. However, it is probably under-recognised and, as a consequence, its burden is underestimated. Here, we report the clinical case of an infant diagnosed with pertussis, despite a regular schedule of vaccination, thanks to a careful clinical evaluation, including personal and family history. In addition to pointing the attention on a precocious diagnosis of atypical cases of pertussis, this case report further raised the issue of modifying and/or implementing the immunisation strategy, considering the ongoing changes of social (eg, immigration) and sanitary (eg, vaccine coverage) background in Italy and all over the Europe.

Protecting newborns from pertussis: The role of partner vaccination in the era of maternal immunization

OBJECTIVE(S)

While antenatal vaccination is the most effective strategy to reduce newborn pertussis infection and its associated morbidity and mortality, uptake has consistently been reported to be suboptimal. "Cocooning" or vaccination of the close contacts of newborns therefore remains an important strategy for protecting newborns when maternal vaccination has not occurred or with insufficient time for antibody transfer. This study assesses the uptake of pertussis vaccination by parents and close contacts of newborns providing insight into the vulnerability of newborns to pertussis upon discharge from hospital to their primary carers.

STUDY DESIGN

The study was conducted at three public and two private hospitals in Melbourne, Australia. A survey was administered to 689 women and/or their partners admitted on maternity wards of participating hospitals after delivery of a healthy newborn between August and December 2016. The main outcomes measured were reported vaccination rates and factors associated with uptake of pertussis vaccination. Kappa statistic and logistic regression were used to determine factors associated with vaccination.

RESULTS

70% of women and 66% of partners reported pertussis vaccination according to national recommendations. Significantly 22% of newborns were discharged to a household where neither parent reported vaccination. Compared to when maternal vaccination did occur, in families where it didn't there were low rates of vaccination of partners (83% vs 26%) and other carers, particularly carers usually resident overseas (76% vs 18.5%).

CONCLUSION(S)

While the majority of mothers and partners reported pertussis vaccination in accordance with recommended guidelines, concerningly nearly a quarter of newborns were discharged to a home where neither parent was vaccinated. When maternal vaccination did not occur, rates of vaccination of the other close contacts was poor. Educating women to encourage vaccination of partners and carers particularly those coming from overseas, prior to their arrival is an important consideration when maternal immunization does not occur. Cocooning remains an important approach to protect newborns of mothers vaccinated late or not vaccinated in pregnancy.