Exclusion criteria were not entirely consistent across studies, resulting in baseline differences across study groups. AZD8329 weeks between vaccination and delivery is required to achieve the highest cord blood antibody levels. The models show that vaccinating earlier than these timeframes will also provide the infant with NR4A3 equally high antibody levels at birth. Conclusions Vaccinating in the second and early third trimester results in the highest antibody levels at birth. Vaccinating earlier within this window is needed to provide equal benefits to both term and preterm born infants. Keywords: Tdap, vaccination, pregnancy, timing, multi-country AZD8329 analysis Background Despite the availability of successful universal pertussis immunization programs, the World Health Organization (WHO) reported in 2014 an estimated 24.1 million pertussis cases and 160,700 pertussis related deaths in children below 5 years of age (1, 2). As most national immunization schedules only recommend pertussis containing vaccines to be administered from 6-8 weeks of age, infants below 2 months of age remain unprotected against pertussis. Therefore, the highest incidence, hospitalization and mortality rates are observed in this population (3, 4). Vaccination with a tetanus, diphtheria, acellular Pertussis (aP) (Tdap) vaccine during pregnancy is being implemented in an increasing number of countries to combat neonatal pertussis-related morbidity and mortality. Administering a Tdap vaccine during pregnancy prompts an immune response in women resulting in an increase in pertussis-specific antibody levels which are transferred to the foetus through the placenta. This yields improved infant immunity in the AZD8329 first months of life and offers protection against pertussis disease (5, 6). Although Tdap vaccination during pregnancy is implemented in many countries, national health services tend to recommend their own optimal window to vaccinate during pregnancy. There is no consensus in national recommendations as the optimal timing to vaccinate during pregnancy to convey maximum immunity to the infant (7C10). Most countries recommend vaccination in the late second or third trimester of pregnancy. However, more recently several countries have recommended vaccinations earlier in pregnancy to reach as many pregnant women as possible with the UK recommending as early as 16 weeks gestational age. Vaccination after 36 weeks has been found less effective as although antibody levels reach a maximum 2 weeks after vaccination, additional time is required AZD8329 for these antibodies to pass to the infant (11). This multi-country analysis investigates the effect of timing of Tdap AZD8329 vaccination during pregnancy on pertussis-specific infant antibody levels at birth in both term and preterm born infants to define an optimal timeframe for vaccination in pregnancy to achieve high antibody titers at birth in all neonates. The first aim (Aim 1) of the study was to determine the effect of gestational age at vaccination (GAV) on infant pertussis antibody titers at birth in term born infants. Secondly (Aim 2), we determined the effect of the interval between vaccination and delivery on infant pertussis-specific antibody titers at birth in both term and preterm born infants. Methods Study Population This multi-country analysis utilises data from four parent studies conducted in either Belgium, Vietnam or Thailand (9, 12C15). All parent studies were prospective cohort studies looking at the effect of Tdap vaccination during pregnancy on maternal and infant immune responses. The study population of the four parent studies was divided into five study groups for this analysis according to the differing protocols of the original study ( Table?1 ). Table?1 Overview of the study groups (BE1: Belgium 1; VN1: Vietnam 1; TL1: Thailand 1; BE2: Belgium 2; BE3: Belgium 3). function (R-package: function. Continuous variables were assessed for collinearity. Covariates exhibiting a moderate correlation or greater were not included in the same model (20). Results of the LMMs are presented as graphical representations, keeping stated variables constant to visualise the effect of timing of vaccination during pregnancy on cord antibody titers. CIs were calculated using the (R-package: with with with with with with exposures to high antibody concentrations (26). When including preterm born infants in the analysis, the results.