Does maternal immunization blunt the effectiveness of pertussis vaccines in infants? Too early to tell

Pertussis, a highly contagious respiratory infection primarily caused by the bacterium Bordetella pertussis , remains a public health priority largely because of the persistently high disease burden in infants too young to be vaccinated. To protect this vulnerable demographic, maternal immunization during pregnancy has been adopted in an increasing number of countries over the last decade. Although this strategy is effective at protecting unvaccinated newborns, it has been demonstrated to cause immunological blunting, whereby maternal antibodies reduce the infant’s immune response to pertussis vaccines. However, the clinical and epidemiological consequences of immunological blunting remain unclear. To illuminate these consequences, we first reviewed the epidemiological evidence for the blunting of vaccine effectiveness after primary immunization of infants. Of the four studies identified, all had short-time monitoring (range: 2–6 years), and their results were heterogeneous, with some estimates consistent with blunting. Next, to better interpret this epidemiological evidence, we extended a previously validated model of pertussis transmission by incorporating maternal immunization with varying degrees of blunting, assumed to reduce the vaccine effectiveness in infants born to vaccinated mothers. Our simulations show three results. First, we find evidence for a transient phase lasting at least a decade after the start of maternal immunization, during which the long-term epidemiological impact of blunting is masked. Hence, ignoring these transient dynamics results in an overestimation of the effectiveness of maternal immunization. Second, because of this transient effect, we show that current empirical estimates may be consistent with a modest level of blunting, amounting to a 10–20% reduction in vaccine effectiveness. However, the large between-study heterogeneity and within-study statistical uncertainty preclude a definitive conclusion, urging for more research to infer the degree of blunting, if any. Ultimately, we predict that, regardless of the degree of blunting, maternal immunization remains effective at reducing pertussis in unvaccinated newborns, supporting the continued use of this strategy to protect this vulnerable population. More generally, our results suggest that maternal immunization can result in an infection-control trade-off between age groups, of practical relevance to many other vaccine-preventable diseases. ### Competing Interest Statement Prof. Pejman Rohani received funding from Sanofi Pasteur France for another project. ### Funding Statement This study did not receive any extra-mural funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes This is a simulation study