Understanding vaccination resistance: Vaccine search term selection bias and the valence of retrieved information

Highlights

• The search terms parents use to find childhood vaccine information biases what they find.

• A search for vaccination-related “risks” retrieves websites that spread 4.8 times more myths than a search for “benefits.”

• The discredited “vaccines cause autism” myth would be encountered almost exclusively by researching vaccination “risks.”

• A search for “risks” will retrieve websites on which 1.6 myths are countered for each myth perpetuated.

• A search for vaccination-related “benefits” will retrieve websites that counter 7.2 myths per myth perpetuated.

Abstract

Context

Dubious vaccination-related information on the Internet leads some parents to opt out of vaccinating their children.

Objectives

To determine if negative, neutral and positive search terms retrieve vaccination information that differs in valence and confirms searchers’ assumptions about vaccination.

Methods

A content analysis of first-page Google search results was conducted using three negative, three neutral, and three positive search terms for the concepts “vaccine,” “vaccination,” and “MMR”; 84 of the 90 websites retrieved met inclusion requirements. Two coders independently and reliably coded for the presence or absence of each of 15 myths about vaccination (e.g., “vaccines cause autism”), statements that countered these myths, and recommendations for or against vaccination. Data were analyzed using descriptive statistics.

Results

Across all websites, at least one myth was perpetuated on 16.7% of websites and at least one myth was countered on 64.3% of websites. The mean number of myths perpetuated on websites retrieved with negative, neutral, and positive search terms, respectively, was 1.93, 0.53, and 0.40. The mean number of myths countered on websites retrieved with negative, neutral, and positive search terms, respectively, was 3.0, 3.27, and 2.87. Explicit recommendations regarding vaccination were offered on 22.6% of websites. A recommendation against vaccination was more often made on websites retrieved with negative search terms (37.5% of recommendations) than on websites retrieved with neutral (12.5%) or positive (0%) search terms.

Conclusion

The concerned parent who seeks information about the risks of childhood immunizations will find more websites that perpetuate vaccine myths and recommend against vaccination than the parent who seeks information about the benefits of vaccination. This suggests that search term valence can lead to online information that supports concerned parents’ misconceptions about vaccines.

Introduction

Growing apprehensions about the risks of vaccines among the general public [1] have been accompanied by more frequent outbreaks of vaccine-preventable disease [2], [3]. Concerns about vaccine safety lead some parents to postpone vaccination of their children, against the recommendation of their pediatrician, while other parents reject all vaccinations for their children [4], [5], [6]. These concerns motivate many parents to seek information about vaccines from other parents, traditional media, and the Internet [7]. A survey of providers found that fear of side effects presented in the media was the most common reason given by parents for refusing vaccines [8].

The Internet may be partially responsible for low child vaccination rates. Vaccination-refusing parents are more likely to have obtained information about vaccines from the Internet than parents who have their children vaccinated [8], [9]. Kata found that a reliance on Internet-based information is problematic due to the presence of inaccurate and deceptive online information [9]. Zimmerman and colleagues found that websites often erroneously link vaccinations to chronic diseases and adverse reactions [10], thereby proliferating vaccine myths. Myths perpetuated online undermine vaccination programs by lowering the public's perceived effectiveness and safety of vaccines [11], [12].

There is evidence of a selectivity effect in online vaccine information searches in which search terms varying in valence yield information that differs in accuracy and tone [13]. People often seek information to support existing beliefs [11], [14]. This confirmatory bias has also been found in online health information-seeking behavior [12]. In the domain of vaccination, a confirmatory bias is illustrated by both the pro-vaccine parent who searches “vaccination benefits” and the parent whose skepticism about vaccination leads to a search for “vaccination risks.”

The purpose of this study is to determine if online search strategies employing negative, neutral, or positive search terms lead to content that correspond with the valence of those terms. We know of no study that has investigated this question. We thus carried out a content analysis that addressed four broad research questions: (a) What vaccine myths are most likely to be perpetuated online? (b) How often do vaccination websites counter myths about vaccination safety and effectiveness? (c) Do websites that discuss vaccination make explicit recommendations about childhood vaccination, and if so, what are these recommendations? (d) Does the online information retrieved about vaccination differ depending on whether the search terms used are negative, neutral, or positive?