ReviewParental decision-making in childhood vaccination
Introduction
There is currently a drop in vaccination coverage against measles, mumps and rubella (MMR) in the UK which may lead to reduced herd immunity and large-scale outbreaks [1], [2] of serious diseases. Measles outbreaks, for instance, are likely to result in some children's deaths and lifelong disability in others. Parental concern about vaccines appears to be the main cause of the drop. In a UK study, around 70% of parents had concerns about MMR [3] and many chose to avoid vaccinating or choose single agent vaccines [4]. In parts of London, less than half of 5-year-old have had a full MMR course [5], well below the level at which outbreaks of vaccine preventable disease (VPD) are likely to occur [6].
The current MMR controversy gained strength after suggestions of a possible link between MMR and inflammatory bowel disease and perhaps autism received wide media coverage [7]. Parental concerns continue despite subsequent studies showing no link between MMR and autism [8], [9], [10] or inflammatory bowel disease [11]. This is not the first time parents have become concerned about vaccines; for example, similar concerns surrounded pertussis in the UK during the 1970s and 1980s [12]. Nor are concerns about vaccine safety in respect of children limited to the UK. A recent US study suggested that 15% of adults believe vaccines are unnecessary to prevent disease and that 61% believe that childhood vaccines are at least somewhat unsafe [13]. Recent concerns about the safety of polio vaccine in Nigeria led to a regional outbreak and severely set back a polio elimination programme [14].
Parental concerns are not the only factors affecting vaccine uptake. As with other types of healthcare, the poor are less likely to vaccinate. The direct and indirect costs of accessing healthcare and poor access to healthcare are important factors [15]. In the case of MMR, however, it is well-off parents who have more concerns and lower uptake [16]. The role of healthcare professionals in relation to vaccine uptake has also received attention. It is claimed that in 78–97% of cases where children attend a clinic and do not receive appropriate vaccinations, this is due to failures by professionals [17], [18] either through lack of information, ambivalence towards the vaccine or fear of litigation following any adverse event [19], [20]. However, these figures are based on routine vaccinations and may not apply where a vaccine has attracted controversy.
Just as parental concern is not the only factor in vaccine uptake so there is not a perfect match between parental concern and vaccination uptake. Ramsay et al. [3] found that even though 70% of UK parents had concerns about MMR, the majority still intended to vaccinate. Nonetheless, if parental concerns are raised, they can lead to a major reduction in vaccination rates. It is, therefore important to understand how parents consider possible risks associated with vaccination and the process by which they decide whether to have their children vaccinated. In this paper we review what is known about the genesis and maintenance of such concerns over risk and how available evidence fits into what is known about people's thinking about risk and probability.
Section snippets
Taking risky decisions
People take decisions frequently about all sorts of things, often fairly automatically, without much conscious thought. For most decisions, whether it be what dish one will choose in a restaurant, or whether a house will prove affordable or, with a rise in interest rates, bankrupt the buyer, available information is incomplete and of variable quality. Such problems cannot be solved through conventional mathematics and the mathematics of risk is, in any case, beyond most people's abilities. The
The nature of the evidence
There are problems not simply with the way in which evidence about vaccines is presented by the media but also with the nature of the evidence itself. Higher vaccine coverage leads to fewer VPDs and more VAEs. Few people in the UK are likely to be able to recall seeing or hearing of cases of serious sequelae from many vaccine preventable diseases [30], [31]. Diseases such as polio have been eradicated in the UK as a result of vaccination. If VAEs are proportional to the number of vaccinations
Other biases
It is well known that when people consider the risks from diseases, they consider not only the incidence of the disease but their personal susceptibility [34], based on representations of the sort of person who might be more or less susceptible to a particular disease. This fits in well with the use of an anchor and adjust approach to risk estimation. Children, especially younger children, are often perceived to be particularly susceptible to particular diseases. The view that children are
Taking a decision
Having formed an impression of the risks associated with vaccination and/or non-vaccination a parent still has to make a decision about whether to vaccinate. This might seem to be a simple accounting matter, costs versus benefits. However, the costs and the benefits are not easily compared because they lack a common ‘currency’ (for instance, comparing a small possible risk of autism versus a larger but still small risk of death). People also show systematic biases in their preferences for costs
Implications
In this paper we have explored what is known about childhood vaccination in the light of decision theory. If our analysis is correct, it has important implications for the problem of encouraging parents to vaccinate their children, assuming that there is strong scientific evidence that such a strategy is likely to prove optimal in protecting the children's health [12]. It is repeatedly suggested in the literature that simply providing better information to parents will cause them to vaccinate
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