The initial search strategy returned 41,570 titles and abstracts, of which 23,201 were removed as duplicates. Title and abstract screening identified 673 full text items for review. Of these, 116 met the inclusion criteria (Figure 1). A review of the included articles’ reference lists did not identify any additional items for inclusion.
Summary of included studies
Of the included studies, 99 (85.3%) used a cross sectional study design (Table 1). Sample sizes across all 116 included studies ranged from 49 to 12,259 participants, with a median of 455 participants. Parental attitudes and beliefs about childhood vaccines in general were studied in 57 (49.1%) studies; and attitudes and beliefs about influenza vaccination (including pandemic H1N1 influenza) in 35 (30.2%). The other 24 (20.7%) studies asked participants about attitudes and beliefs for other specific vaccines, such as polio and rotavirus vaccines.
Thirty-four countries were represented in the included studies (Figure 2). The most common country in which studies were conducted was the United States (n=36), followed by Canada (n=9) and the United Kingdom (n=8). When aggregated by the number of participants, the United States included the largest number (40,155 participants), followed by Canada (7,200 participants), and the United Kingdom (3,273 participants).
Use of questionnaires and survey instruments
The questions asked of participants varied substantially across the set of included studies. There was heterogeneity both in terms of the specific questions asked of participants as well as the provenance of those questions in theory or from standardised questionnaire sets.
The most commonly used standard questionnaire was the Parent Attitudes about Childhood Vaccines (PACV) Survey Tool, used in 4 studies with its full format with 15 questions (15-18). In some studies, the PACV questions were adapted to match the local context or study population, such as in Malaysia (17) and for expectant parents in the United States (15). In 2 studies, a subset of the PACV questions were used (19, 20). Other questionnaires used included 7 studies based on national immunisation surveys or health department of health questionnaires (21-27), 1 study based on the Parental Attitudes toward MMR Vaccine and Trust in Medical Authority questionnaire (28), and 1 that used the Vaccine Safety, Attitudes, Training and Communication measures (29).
A total of 62 (53.4%) included studies developed questionnaires by reviewing previous literature or using previously developed questionnaires and/or frameworks, 4 developed questionnaires with experts in the field, 1 used a self-developed scale, and 1 conducted a pre-study qualitative evaluation of the target population to elicit appropriate questions. The remaining 48 studies did not report having used previous examples as the basis for the designs of their questionnaires.
A variety of theoretical frameworks were used to inform the design of the questionnaires used in the studies. The most common was the Health Belief Model (HBM), which was explicitly stated as having been used to inform the questions in 22 (19.0%) studies (26, 28, 30-49), followed by the Theory of Planned Behaviour, which was used in 5 (4.3%) studies (50-55). Other studies that were adapted from existing questionnaires may have implicitly been based on these or other theoretical frameworks as a consequence of having adapted from other questionnaires but did not explicitly claim the theoretical framework as a basis for their questions.
Questions about intention to vaccinate or vaccination status
Of the 116 included studies, 38 (32.8%) included questions in which parents were directly asked about their vaccination intentions for one or more antigens. The specific questions that were asked varied across the set of studies. Examples included, “If you had another infant today, would you want him or her to get all the recommended shots?, “I would get a flu vaccine for my child under 5, every year, if it was free”, and “If your child were offered it at some point in the future, would you vaccinate them against swine flu?”. This variation precluded a synthesis of the results, and the proportion of participants responding in the affirmative varied substantially across the set of studies.
Among the 16 (13.8%) studies in which parents were directly asked about whether they would have children vaccinated for all childhood vaccines, the percentages ranged from 75% in a study involving 200 parents in the United States (56) to 98% in a study involving 54 parents in Canada (31). For the 9 (7.8%) studies that asked about intentions in relation to influenza vaccination, the percentages ranged from 29% in a study involving 236 parents in Canada (57) to 92% in a before and after study at a clinic involving 5,284 and 5,755 different groups of parents in rural Kenya (58).
Associations between attitudes and beliefs with vaccination intentions or vaccination status
We identified 13 (11.2%) studies reporting on the association between attitudes and beliefs with vaccine intentions. All of these studies identified a significant association between attitudes and beliefs with intentions. In 8 of the 13 studies, associations were found for questions related to the severity of the disease (18, 21, 30, 32, 38, 59-61), and these studies were conducted in the United States (n=3), the Gambia, Israel, Germany, the United Kingdom and Sweden. In 7 of the 13 studies, associations were found for questions related to the susecptability of the disease (18, 21, 30, 32, 38, 45, 53), and these studies were conducted in the United States (n=2), the Gambia, Israel, the Netherlands, the United Kingdom and South Korea. In 4 of the 13 studies, associations were found for questions related to the efficacy of the vaccine (21, 43, 61, 62), and these studies were conducted in the United States, Canada, Italy and Sweden. In 3 of the 13 studies, associations were found for questions related to safety of the vaccines (18, 60, 62), and these studies were conducted in the United States (n=2) and Italy.
Among the 116 included studies, 57 (49.1%) reported on the association between attitudes and beliefs with vaccination status. All studies identified an association between attitudes and beliefs with vaccination status, with concern about safety and efficacy the most commonly reported associations with lower vaccine uptake. In 26 of the 57 studies, an association between vaccination status and beliefs about the safety of vaccines were identified (29, 39, 40, 48, 49, 55, 63-83) and these studies were most commonly conducted in the United States (n=9) and China (n=4). Among the 26 studies that found an association between vaccination status and beliefs about the safety of vaccines, participants were asked about all childhood vaccines in 10 studies (55, 63, 67-72, 74-76), and about influenza vaccines in 12 (39, 40, 49, 64-66, 73, 77, 79-81, 83). In 10 of the 57 studies, an association was found between belief in the efficacy of the vaccine with vaccination status (24, 39, 47, 64, 73, 77, 80, 82-84), and these studies were most commonly conducted in Israel (n=3) and Japan (n=2). Of the 10 of 57 studies that found an association between belief in the efficacy of the vaccine and vaccination status, 2 investigated all childhood vaccines (24, 84), and 7 investigated attitudes and beliefs about influenza vaccine (39, 47, 64, 73, 77, 80). In 11 of the 57 studies, an association was found between vaccination status and trust in doctors and health care professionals or recommendations from a doctor (24, 41, 66, 69, 80, 85-89). Of those, 6 participants were asked about all childhood vaccines (24, 68, 69, 85-87), and influenza vaccines in 4 studies (41, 66, 80, 88).