The association between maternal mental health and vaccination uptake and timeliness during early childhood.

Background: Uptake of routine childhood immunisations has been declining over the last ten years, resulting in occasional outbreaks of measles or pertussis. It remains unclear when vaccines are missed or delayed and how this is associated with outbreaks. A wide range of different factors influence parental decision-making around vaccinations. However, the role of maternal mental health conditions on vaccine uptake in early childhood remains unclear. Objectives and data sources: The objectives of this thesis were: 1) to summarise the existing evidence on the association between mental health issues and vaccine uptake in general; 2) to develop and validate a method to best assess childhood immunisations in routinely collected electronic health records; 3) to describe different patterns of vaccine uptake and delay in children up to age five; 4) to explore the role of vaccine timing versus improved coverage during early childhood on the risk of measles outbreaks; 5) to explore the role of maternal mental health issues on vaccine uptake and timeliness in early childhood. All analysis for objectives 2-5 used electronic health records from the Clinical Practice Research Datalink (CPRD). Results: The results from 23 studies included in the systematic review indicated a complex relationship between mental health and vaccine uptake (Chapter 3), that was highly dependent on definitions and ascertainment of both mental health issue and vaccination. Using a cohort of children born between 2006 and 2014 registered in CPRD, my algorithm to identify immunisation records was validated against national coverage estimates and found comparable results (Chapter 7). Using this algorithm in a cohort of 573,015 children under five, there was evidence of lower coverage and more delay the later a vaccine was recommended in the immunisation schedule (Chapter 8). Simulating different vaccination strategies on the same cohort of children, an increase of vaccine coverage by 1% for the first MMR vaccine could reduce measles cases by 29% but might be difficult to implement. However, an earlier second dose of the MMR dose could reduce cases still by up to 20% (Chapter 9). Among 397,510 mother baby pairs, children of mothers with common mental disorders had lower odds of being vaccinated at the age of two (aOR 0.95, 95%CI: 0.93-0.98) and five (aOR 0.86, 95% CI 0.84-0.89) compared to children of mothers with no recorded mental health conditions, regardless of the timing of recording of the mental health issue. There was a particularly low odds of vaccine uptake at the age of five for children of mothers with combined common mental disorder and substance use disorder (aOR 0.70, 95% CI: 0.62-0.78) but no difference for children of mothers with severe mental illness. Conclusions: Vaccine coverage and timeliness decreased with increasing age of a child. Coverage was more important than timeliness to prevent measles outbreaks. Inequalities in vaccination coverage associated with maternal mental illness also grew with increasing age of the child. Extending support services for women with mental health issues beyond the child’s first year of life could offer potential to improve vaccination uptake and reduce childhood infections.