Factors that Influence Vaccination Decision-Making among Pregnant Women: A Systematic Review and Meta-Analysis

"Understanding the influence of personal beliefs and experiences on maternal vaccination uptake is key to designing, testing and deploying interventions that are tailored to improve vaccine acceptance and coverage in routine and outbreak settings."

Consensus within the field and across 4 prior literature reviews indicates that receiving a recommendation from a health care professional (HCP) for vaccination is the most important factor in a woman's decision-making about antenatal vaccines, irrespective of geographic or social context. However, where data are available, one-third of pregnant women remain unvaccinated despite receiving a recommendation. Therefore, this systematic review and meta-analysis sought to understand the significance of factors other than HCP recommendation and to distinguish between vaccines administered routinely and during outbreaks (e.g., COVID-19), when concern of disease risk may be amplified but concerns about using a novel vaccine may also be enhanced.

The researchers searched MEDLINE, Embase Classic & Embase, PsycINFO, CINAHL Plus, Web of Science, IBSS, LILACS, AfricaWideInfo, IMEMR, and Global Health databases to identify qualitative and quantitative studies that reported on the cognitive, psychological, and social factors associated with maternal vaccination among pregnant and recently pregnant women (within 2 years of birth). They identified 120 studies from 30 countries published prior to November 22 2018 for inclusion; of these, 49 studies were eligible for meta-analysis.

This process revealed 8 categories of factors that influence maternal vaccination across both qualitative and quantitative studies: accessibility and convenience (55 studies), personal values and lifestyle (43), awareness of information regarding the specific vaccine or disease of focus (90), social influences on vaccine use (109), emotions related to vaccination (85), perceptions of vaccine risk (110), perceptions of vaccine benefit (93), and personal vaccination history (80). They used random-effects models to calculate pooled odds ratios of being vaccinated by vaccine type.

Selected quantitative findings included:

• The odds of receiving a pertussis or influenza vaccination were 10-12 times higher among pregnant women who received a recommendation from HCPs. During the 2009 influenza pandemic, an HCP recommendation increased the odds of antenatal H1N1 vaccine uptake 6 times.
• The odds of pregnant women receiving season influenza vaccination were 5 times higher if they had general information about the vaccine. Similarly, the odds were 3 times higher among pregnant women who knew there was a national vaccination policy in place versus women who were unaware (thus, publicising such policies "could improve trust in maternal vaccination programmes and facilitate improved uptake").
• Believing there was potential for vaccine-induced harm had a negative influence on seasonal and pandemic influenza vaccine uptake, reducing the odds of being vaccinated 5-fold. Having concerns about pandemic influenza vaccine side effects in general was associated with 2 times lower odds of vaccination; having knowledge of specific pandemic influenza vaccine side-effects (defined as a awareness of a known adverse reaction as outlined by the drug company label insert, e.g., fever) was associated with 3 times lower odds of vaccination.
• The odds of being vaccinated were 8 times higher when pregnant women believed that the pandemic influenza vaccine benefits the mother. The odds of accepting the seasonal influenza vaccine were 7 times greater when pregnant women perceived the vaccine as generally effective, 3 times greater when they believed the vaccine benefits the mother, and almost 2 times greater when they believed the vaccine benefits their baby.

Selected qualitative findings include:

• Participants expressed willingness to receive information from HCPs, but were disappointed with a perceived overuse of leaflets to convey information in lieu of direct conversation with an HCP. Some pregnant women sought vaccination information through media or the internet, but these avenues were not regarded as the most reliable for accurate information.
• Almost all qualitative studies indicated that being aware of maternal vaccination and/or the respective disease, regardless of information source, was key to receiving the vaccine but rarely sufficient (17 studies). Furthermore, 16 qualitative studies highlighted an information gap specific to knowledge of vaccines during pregnancy, reflecting a general lack of awareness among pregnant women of maternal vaccine recommendations and benefits.
• While 16 studies mentioned the benefits of antenatal vaccines, 11 of these studies reported there was also doubt and uncertainty around the usefulness or the efficacy of vaccines in pregnancy.
• In some studies, participants may have accepted vaccines generally, but not during pregnancy. Community rumours and cultural values were found to influence views on vaccination among pregnant women. In addition, several studies reported preferences for natural immunity or a healthy lifestyle during pregnancy as reasons to decline vaccinations.
• Pregnant women feared the unknown, the disease (particularly for pandemic influenza), vaccine harm or side effects, vaccine safety, and pain. One study reported that vaccinated and unvaccinated pregnant women expressed similar fears, but unvaccinated women often described their fears in more detail.

Thus, consistent with the extensive body of evidence on this topic, an HCP recommendation for routine vaccinations (seasonal influenza and pertussis vaccination) was a very strong factor influencing maternal vaccine acceptance. However, the effect of an HCP recommendation during an outbreak, whilst still powerful, may be muted by other factors. This suggests the need for further research, particularly when vaccines are novel.

There was some evidence to support an association between perceptions of the severity of pandemic influenza and pregnant women's vaccination status with the belief that pandemic influenza can result in hospitalisation, increasing vaccine uptake 3-fold. The researchers recommend additional studies to explore the role of disease severity and susceptibility in greater detail to clarify their importance when other factors are present.

The researchers assert that study's findings have implications for public health communication strategies around maternal vaccination, since campaigns, particularly during an epidemic or influenza outbreak, have centred around disease threat. The researchers caution against any communication approach that highlights only the threat of disease when publicising vaccination. They call for further review of the messaging strategies comparing those with and without explicit details of vaccine safety to the public and/or a discussion of disease threat with attention to language that might inadvertently promote fear. ("Whilst it is essential that pregnant women are informed about the risks of the disease in order to be appropriately consented, the manner in which this is communicated should be evaluated. It appears that, in some cases, fear may be counter-productive. This has been seen in childhood vaccines: if parents already fear the vaccine, making them fear the disease leads to decision conflict, and hesitancy...")

The findings may also have implications for future study design. Many studies included in this systematic review and meta-analysis were designed using the framework of the Health Belief Model (HBM). In brief, the HBM describes final vaccination acceptance or rejection based on the interacting beliefs of seriousness and susceptibility to the target disease of the vaccine, benefits of the intervention, and barriers in order to predict health behaviour. The present study suggests that the model should be adapted to highlight the importance of the latter 2 categories in maternal vaccination behaviour predictions.

The researchers note that data on specific concerns during pregnancy are often unavailable to general practitioners or midwives during counselling. Thus, they recommend that HCPs are given ready access to clear and concise language on the safety of vaccines during pregnancy. In addition, there is limited availability of summarised reports for the public or general practitioners that synthesise the abundance of safety evidence on miscarriage, infertility, and birth defects. Health bodies should make this widely generated safety evidence more accessible to the public and to HCPs to facilitate uptake where concerns in practice arise, according to the researchers.

In conclusion: "Based on the results of this review, interventions designed to impact maternal vaccine uptake should continue to encourage individualised HCP recommendations. Additionally, personalised counsel on the benefits and safety of a vaccine should emphasize the vaccine's protective effect on the pregnancy as well as discuss implications for foetal and childhood development. This is in contrast to traditional communication on disease threat in isolation."