Introduction
There has been a global resurgence in pertussis in recent years, with
the highest rates of hospitalization and death in infants too young to
be fully protected by routine childhood vaccination
series.1-3 Infection of young infants occurs primarily
through household contacts, with new mothers identified as the most
common sources of transmission.4 Pertussis vaccination
during pregnancy protects the mother from pertussis infection but more
importantly offers passive immunity to her newborn via transplacental
transport of maternal antibodies and is currently considered the most
successful and effective intervention to prevent early infant
disease.5 Maternal pertussis vaccination at least
seven days before delivery has been shown to protect against pertussis
in up to 91% of infants in the first two months of life.6, 7 Following the implementation of government funded
maternal pertussis vaccination programs for pregnant women in different
countries there has been an increasing general pertussis vaccine uptake
in pregnancy.8 However uptake varies across and within
countries in pregnant women and is suboptimal.8 One of
the reasons for low pertussis vaccination uptake is healthcare
providers’ and/or women’s concerns about the safety of the vaccine
during pregnancy.9, 10
Several systematic reviews11-14 have demonstrated that
maternal pertussis vaccination during pregnancy does not adversely
affect obstetric or neonatal outcomes, although the quality of the
evidence in underlying studies is low. Many previous studies have
investigated the safety of pertussis vaccination during pregnancy
retrospectively, due to the relatively cheaper cost, fewer ethical
concerns, and difficulty in recruiting pregnant women to randomized
controlled trials. Three retrospective cohort studies15-17 reported a small but statistically significant
increased relative risk of chorioamnionitis in women who had received
pertussis vaccination during pregnancy. This unreplicated finding merits
further investigation since chorioamnionitis is associated with severe
short-term and long-term neonatal complications.18Most observational studies have been unable to account for the
time-dependent nature of exposure to pertussis vaccination during
pregnancy. To accurately determine any risk of maternal pertussis
vaccination for pregnant women and their infants, prospectively designed
studies incorporating statistical approaches suitable for analysing
time-dependent associations between maternal pertussis vaccine exposure
on pregnancy and birth outcomes are warranted. The primary aim was to
prospectively assess pregnancy and birth outcomes following pertussis
vaccination during pregnancy considering time‐dependent vaccine exposure
and using the most comprehensive set of potential confounding variables
considered to date.