Introduction
Undoubtedly, vaccines may be perceived as one of the most important discoveries in the history of contemporary medicine [1]. Though every invention has its assets and flaws, the latter are relatively infrequent in the case of vaccines. According to the statistics from the Health Resources and Services Administration’s report on the matter of the National Vaccine Injury Compensation Program, in the years 2006-2019, over 4 billion doses of vaccines were administered in the USA, which were implicated in compensation (due to severe injury) in less than 6000 cases [2]. In conclusion, the prevalence of severe injuries due to vaccination was approximately 1.5 cases per 1 million doses.
On the other hand, vaccines are said to save millions of lives every year [3]. For example, before the year 1942 – in which mass immunization against diphtheria was introduced in the UK – the average number of cases was about 60 thousand [4]. Between 2009 and 2017, these numbers decreased to 1-7 cases per year [5]. Even more remarkable is that due to the vaccination program, humanity managed to eradicate smallpox [6] – as this single disease is said to have been the cause of 300-500 million deaths in the 20th century alone [7].
Regrettably, recent years have seen a decrease in the percentage of vaccinated children [8, 9] and the spread of anti-vaccination movements’ propaganda [10]. Several studies show that undervaccination may result in sudden outbreaks of infectious disease epidemics [11, 12]. Thus, it is crucial to identify the underlying causes of vaccine hesitancy and start reacting against them.
Still, there is not enough research among young people concerning this problem. Students are an essential group to analyze, as, in the near future, they will probably become parents and will be presented with a choice whether to vaccinate their children or not. Moreover, the assumption that their knowledge levels should be significant may be made in their case.
Considering the issues mentioned above, the aims of this research were:
- to measure the scale of vaccine hesitancy among Polish students;
- to investigate the reasons for negative attitudes toward vaccinations;
- to analyze possible relatedness between the level of knowledge about vaccines and the students’ trust in their effectiveness.
Material and methods
A non-representative cross-sectional survey was conducted during April-June 2021 with a self-administered questionnaire among 301 undergraduate students (229 female, 71 male, and 1 non-binary) from Polish universities. The online questionnaire with 28 questions (see Webappendix 1) was prepared using MS Forms (Microsoft, USA) and disseminated to potential participants via social networks and institutional e-mail addresses. Participation in the research was voluntary, and the purpose of the study was explained at the beginning of the questionnaire. The collected data were anonymous. It required about 5-7 minutes to answer all the questions. In order to avoid the impact of the questionnaire structure on the results of the survey, it was carefully analyzed to suggest answers as little as possible (especially in knowledge questions). Additionally, the order of distractors in individual questions was randomly generated for each respondent. The study did not need the approval of the bioethical committee because it was not a medical experiment in accordance with Polish law. Filling in the questionnaire and sending a reply was considered unambiguously as giving informed consent to participate in the study.
Statistical analysis was performed using Statistica 13 software (TIBCO Software, USA). The values of all variables were presented as proportions (percentage). The distribution of data was checked using the Shapiro- Wilk test. The Mann-Whitney U test was used to measure the significance of the difference in comparison of two groups and the one-way analysis of variance (ANOVA) was used in comparison of three or more groups. The p = 0.05 was considered the limit of statistical significance.
Main comparisons between groups were pre-specified before data collection and made based on gender, field of study, university level, sources of knowledge about vaccines, and the respondents’ knowledge about vaccinations. Additional comparisons were made by dividing students into the groups regarding given answers (after the data collection) – whether mercury is a component of vaccines, based on their attitude towards vaccines against SARS-CoV-2 and the experience of developing an illness that a vaccine should protect them against.
Students were divided into groups by the field of study using the Organisation for Economic Co-operation and Development (OECD) classification [13]:
- natural sciences (NAT),
- engineering & technology (ENG),
- medical & health sciences (MED),
- agricultural sciences (AGR),
- social sciences (SOC),
- humanities (HUM).
Considering university level, respondents were categorized into two groups: years 1-3 (bachelor’s degree level) and 4-6 (master’s degree level). This division corresponds to the construct of higher education in the Bologna Declaration, to which Poland is a signatory [14].
The division according to the sources of knowledge about vaccines was done as follows. Out of 6 possible answer options about the sources, half were scientific (“scientific articles and textbooks”, “experts or doctors”, “popular science blogs”), and the other half were unscientific (“information portals, TV, radio”, “social media”, “friends or family”). Based on respondents’ answers, they were divided into five groups:
- those who chose only scientific sources (SCI),
- those who chose more scientific than unscientific ones (MSCI),
- those who chose equal numbers of scientific and unscientific ones (EQL),
- those who chose more unscientific than scientific ones (MUCI),
- those who chose only unscientific sources (UCI).
The division according to the students’ knowledge about vaccines was done as follows, using the results from answers given to 8 questions (No. 9, 10, 11, 12, 13, 26, 27, 28 – see Webappendix 1). Six were a single choice, and the respondents were given 1 point for every correct answer. One question had two correct answers – students were given 0.5 points for each. One question had four correct answers – students were given 0.25 points for each. Gained points were summed up. Based on the score, respondents were divided into four categories of knowledge:
- very poor – 2 points or less,
- poor – more than 2, up to 4 points,
- good – more than 4, up to 6 points,
- very good – more than 6 points.
Results
The general characteristics of the study group are presented in Table 1. The distribution of given answers in the questionnaire is presented in Table 2.
Females vs. males
Significant differences in women’s and men’s answers were infrequent. According to respondents’ statements, men were more likely to gain knowledge about vaccines from popular science blogs than women (47.14% and 31.44%, respectively, p = 0.016). Furthermore, a higher percentage of men than women claimed that their level of knowledge in this matter was sufficient (57.14% and 42.79%, respectively, p = 0.035). Their knowledge testing results did not support this – mean points scored for women = 5.73, and for men = 5.98 (p = 0.071).
Of those who stated that they did not intend to get vaccinated against SARS-CoV-2, significantly more women than men indicated one of the reasons the opinion that the vaccine was not sufficiently tested (10.48% and 2.86%, respectively, p = 0.048).
Only one respondent described himself as non- binary – due to the very small sample, this category was not included in the gender comparison.
Fields of study comparison
A significant difference (p = 0.006) was observed in the question about using scientific articles as a source of information about diseases. The percentage of students who claimed to use them exceeded 58% in all OECD study fields. However, in groups of students studying MED or AGR, the percentage was much higher (84.75% and 81.82%, respectively) than in others. A similar difference was noted in the question about using scientific sources as a source of information about vaccines (p = 0.006). In 4 (NAT, ENG, SOC, HUM) out of 6 fields, the results were quite similar – at least 55% of students claimed to use scientific sources, whereas, in MED or AGR fields, there were respectively 86.44% and 78.79%.
Another significant difference (p = 0.001) was obtained in the question about the trust in the effectiveness of vaccines. In 4 fields (NAT, ENG, AGR, HUM), the percentage of students who claimed to trust vaccines was near 80%, but in the MED, the value was 94.92%, while in the SOC, it was only 65.85%. The results were similar in the question about the willingness to be vaccinated (p = 0.003) – the MED represented the highest, and the SOC represented the lowest percentage of students willing to be vaccinated (94.92% and 65.85%, respectively).
On the other hand, more students of HUM and SOC claimed not to have sufficient knowledge about vaccines (63.89% and 67.07%, respectively), whereas other students (NAT, ENG, MED, AGR) had comparable results approaching 50% (with the exception of the MED group with 40.68%). The p-value was 0.024.
Among students who answered that they considered vaccinating their children only with the obligatory vaccines, the vast majority denied that it was because of a lack of trust towards vaccine manufacturers. However, a significant difference (p = 0.033) was noted for this question because the percentages of AGR and SOC students who denied it did not exceed 90% (as it did in other fields) but were 84.85% and 87.80%, respectively, while the percentage of MED students was 100%.
Table 3 presents data concerning students’ willingness to vaccinate against SARS-CoV-2 depending on their field of studies. Students who claimed they did not want to be vaccinated against SARS-CoV-2 were also asked for an explanation. The majority of each study field group denied the option “I am afraid for my life and health” and agreed with the option “I am afraid for my and my relatives’ life and health.” However, the vast difference was among the MED students – 91.53% claimed not to be afraid for their life and health, and 74.58% denied also being afraid for their and their relatives’ life and health. A noticeable difference was also observed in the answers for the option “The vaccine is not examined sufficiently.” Only the groups of HUM and SOC students agreed with this statement by more than 10% (11.11% and 18.29%, respectively). A noticeable difference was also found for the option “I want to contribute to the ending of the pandemic” since the vast majority of MED students denied this statement, which corresponded with their denial of the option “I want to avoid restrictions related to the pandemic” too.
Another statistically significant difference (p = 0.002) in responses from students of different fields was found in the comparison of their level of knowledge about vaccines.
Years 1-3 vs. years 4-6
No statistically significant differences were found when dividing students into two groups by their university level – bachelor’s degree and master’s degree.
Sources of knowledge comparison
The frequency of using particular sources of knowledge about diseases in the groups mentioned above was different than in the matter of the vaccines. In all the groups, “experts and doctors” was the most popular answer (SCI = 77.78%, MSCI = 92.31%, EQL = 82.46%, MUCI = 80.77%, UCI = 53.13%), but among those who chose only unscientific sources of knowledge about vaccines, the option “information portals, TV and radio” as a source of knowledge about diseases was selected with the same frequency as “experts and doctors” (53.13%).
Another significant difference (p < 0.001) was found in the answers concerning respondents’ trust in vaccines’ effectiveness. The percentage of those who said they trusted in vaccines exceeded 80% in all the groups, except the UCI, where the percentage decreased approximately by half, reaching 43.75%. The results were quite similar when students were asked about their willingness to be vaccinated (both with the obligatory and optional vaccines; p = 0.031) (Figure 1).
The vast majority of participants agreed with the statement that the vaccines which were mandatory in Poland at the time of conducting this research should remain obligatory (p = 0.016). In 3 out of 5 groups, more than 90% of respondents agreed with this sentence (SCI, MSCI, MUCI = 92.59%, 91.03%, 92.31%, respectively). The percentage was slightly lower among the EQL group (84.21%) and significantly lower in the UCI group (71.87%). Significant differences were found in students’ willingness to vaccinate their children (p < 0.001) – see Figure 1 for details.
Those respondents who claimed they did not want to have their children vaccinated at all were asked for the reasons for such a decision (compare with Webappendix 1). In the SCI and the EQL group, all answers were chosen with similar frequency without any significant difference. MUCI more frequently indicated “no trust in vaccine manufacturers” and “no trust in vaccines’ effectiveness,” while in the UCI group, “no trust in vaccine manufacturers” was the most popular reason.
A similar question was posed to those who said they were willing to vaccinate their children only with the obligatory vaccines. In all the groups, except for one (MSCI), “fear of adverse effects following immunization and long-lasting adverse effects” was the most frequently chosen option. In the MUCI group, most respondents stated that “no trust in optional vaccines’ effectiveness” was one of the reasons behind their decision.
Another difference was related to the question whether respondents wanted to get vaccinated against SARS-CoV-2 (or whether they had already been vaccinated) – p = 0.014. Details are presented in Table 3. Those who wanted to vaccinate against SARS-CoV-2, in general, were asked for their motivation. The SCI, MSCI, and UCI groups most frequently indicated their willingness to contribute to the end of the pandemic. In the EQL and MUCI groups, concern for their and their families’ health and life was the prevailing answer. Respondents who claimed they did not want to vaccinate against SARS-CoV-2 at all were also asked for their reasons. Besides the MUCI group, in which no fear of the virus was the most popular answer, the rest indicated no certainty of the vaccines’ safety with the highest frequency.
Students answered significantly differently (p = 0.001) when asked about the possibility of the whole genetic material in the human body being changed by mRNA, which is a component of some of the vaccines against SARS-CoV-2. The fraction of those who agreed with such a possibility was the largest among UCI (28.13%) and the smallest in the MSCI group (2.56%). In the other groups, the following fractions of respondents answered similarly: SCI – 6.48%, EQL – 10.53%, and MUCI – 11.54%.
The last variable with a significant difference (p = 0.004) in this section was the one with students’ levels of knowledge about vaccines. The highest percentage of those who represented the worst level of knowledge belonged to the UCI group (6.25%), while the lowest belonged to the MSCI group (0.00%). Moreover, UCI had the lowest percentage of respondents with remarkably high levels of knowledge about vaccines (21.88%). The MSCI was the best in this comparison (52.56%). For details (Table 3).
Level of knowledge comparison
The trust in the effectiveness of vaccines increased with the level of knowledge (p < 0.001). Those whose knowledge was very poor or poor often answered that they did not trust it (80.00% and 62.07%, respectively) compared to those with good and very good knowledge (23.13% and 6.02%, respectively).
Those whose knowledge was very poor significantly more often (p < 0.001) chose not to vaccinate their children (60.00%) than those with poor, good, or very good knowledge (17.24%, 2.99%, and 0.75%, respectively).
Significantly more (p < 0.001) students with very poor and poor knowledge were not willing to get vaccinated (60.00% and 62.07%, respectively), unlike those with good and very good knowledge, who mostly willingly vaccinated themselves (76.12% and 90.98%, respectively).
Students whose knowledge was very poor or poor significantly more often (p < 0.001) answered that the obligatory vaccines included in the vaccination schedule current at the time of conducting research should not have been obligatory (60.00% and 41.38%, respectively). In comparison, most of those with good or very good knowledge responded that they should have remained compulsory (90.29% and 94.74%, respectively).
There was a significant association between the level of knowledge and the attitude towards investing in developing vaccines against some serious pathogens, such as HIV (p < 0.001). Those with very poor and poor knowledge more often answered against such an investment (40% and 13.79%, respectively) than students with good and very good knowledge (1.49% and 4.51%, respectively).
There was also a significant association (p < 0.001) between the attitude to the vaccination against SARS-CoV-2 and the level of knowledge about vaccines (Table 3).
Other comparisons
Students who did not deny mercury being one of the components of vaccines significantly more often claimed that they did not trust the effectiveness of vaccines (30.2% compared to 17.35% among the others, p = 0.010) and did not undergo vaccination willingly (32.2% compared to 19.00% among the others, p = 0.030). They were also less likely to answer that doctors or experts were their sources of knowledge about vaccines compared to the others (44.07% and 64.46%, respectively, p = 0.004). Moreover, those students more often replied that they did not want to vaccinate their children (11.11%) or that they wanted to vaccinate them only with the obligatory vaccines (43.21%), compared to the other group (1.82% and 14.09%, respectively).
52.16% of respondents stated that they experienced an adverse effect following immunization. There was a significantly higher (p = 0.048) number of students who replied that they did not trust vaccines’ effectiveness among those who answered that they had such an experience (30.19%) vs. those who answered that they had not experienced it (18.14%). In the group of students that experienced the development of an illness that a vaccine should protect against (17.61%), there was a significantly higher (p = 0.011) proportion of those who claimed no willingness to be vaccinated against SARS-CoV-2 (22.64%) versus those with no experience of such an issue (9.67%). The “experienced” group more rarely chose the answer “I want to be vaccinated as soon as possible” (35.45% vs. 47.18% in the “inexperienced” group), and more often, “I want to be vaccinated when I am certain of the safety of the vaccine” (28.3% vs. 23.79% in the “inexperienced” group, p = 0.011).
Discussion
Since education in Poland is compulsory under 18 for each child regardless of gender, their knowledge should not show significant disparity, which was reflected in our results. Moreover, the survey’s findings did not show a significant difference according to university level since the questions concerning knowledge about vaccines were mainly general and did not demand specific schooling in the medical or biological field.
In questions about knowledge concerning diseases and vaccines, trust in their effectiveness and safety, and willingness to vaccinate their children, in which a significant difference was found, the MED group dominated as the one with the best knowledge level and highest trust or willingness to vaccinate children. On the opposite side were usually SOC and HUM groups. This disparity may be due to diverse interests and research backgrounds related to their fields of study. The MED group is more exposed to medical information, including vaccines and diseases, or seeks this kind of information more often than any other group. Furthermore, SOC and HUM groups may concentrate more on working with other people based on their creativity, while the MED group focuses more on facts and evidence gathered by other scientists.
In general, the MED group was most knowledgeable about vaccines, but one would expect 100% of respondents in this group to have reliable knowledge and attitudes on this topic. Unfortunately, many medical schools lack dedicated vaccinology courses, which may be the reason for the mentioned deficiencies in this respect.
Those who mostly relied for their vaccine knowledge on information portals, media, and social media might be prone to anti-vaccination movements’ agenda that uses conspiracy theories and emotional language to impact students’ views on vaccination [15].
According to Betsch et al. [16], visiting a website that contains anti-vaccine content (just for approximately 5-10 minutes) negatively impacts visitors by reducing willingness to vaccinate and increasing distrust of vaccines’ effectiveness.
In our research, similar results were obtained. The dis- cussed group of students more often undermined the effectiveness and safety of vaccines, which could cause some hesitation in the matter of their and their children’s vaccination. Moreover, they were probably open to fake theories about mercury’s presence in vaccines – one of the flagships of an anti-vaccination movement [17] – which was reflected in our study by the answers (of those who did not reject the presence of mercury in vaccines) to the questions about the willingness to be vaccinated, children’s vaccination, trust in the effectiveness of vaccines, and sources of knowledge about vaccines. Also, the group mentioned above rarely expressed a desire to vaccinate against SARS-CoV-2. It is worth noting that pure mercury has never been an ingredient in vaccines. Some old vaccines (no longer available) used mercury salts, such as thiomersal, as an antibacterial and antifungal preservative [18].
Along with the increasing number of such opinions on vaccines [19] and negligence in education about them, society might face the global problem of denying the benefits of vaccines.
Concerning the increasing frequency of children’s vaccination refusal in Poland, the remarkable differences which were noted between students who based their views on non-scientific sources and those whose major source was based on scientific evidence are crucial in the context of their parenthood – since students, future parents, tend to be more influenced by media and the Internet than older people [19, 20]. USCI students’ knowledge was on a much lower level. Also, they more often rejected vaccination against SARS-CoV-2 and more frequently questioned vaccines’ effectiveness and safety of vaccines, in general. Moreover, this group less frequently answered that they wanted to vaccinate their children. That state of affairs could put their children in danger of some rare illnesses, such as measles, which tends to be a more common disease in Poland (339 cases in 2018 and 1492 in 2019) [21] and break the herd immunity. It is alarming, especially because students, in general, are more likely to use scientific sources than the rest of the population.
Regardless of students’ sources of knowledge about vaccines (even if they were only unscientific), considering sources of knowledge about diseases, the most popular answer was “experts or doctors.” We may assume that some of the respondents did not seek out knowledge regarding immunization from experts (even if they did so in the case of diseases) or did not receive such information. Independently of the cause, doctors and other healthcare professionals should remember that they strongly impact patients’ attitudes towards vaccination. The research by Kundi et al. [22] showed that parents followed vaccine recommendations more willingly when their parent-doctor relationship was better – doctors treated them respectfully and gave them enough time to pose questions. It was also essential to explain to parents both the benefits and risks of vaccination [23].
Moreover, our results showed that the MSCI group had a higher knowledge level than the SCI group, which may reflect the impact of social media in which medical professionals are more present and have remarkable opportunities to share scientific knowledge among all. Unfortunately, according to a survey by Davis et al. [23], approximately one-quarter of doctors believed that informing parents about risks may be unnecessarily alarming. Further healthcare professionals’ education should be focused on the fact that their actions are very significant for the problem of vaccine hesitancy.
Our results indicated that medical professionals (“experts and doctors”) were the most popular source of knowledge about health and diseases despite the respondents’ preferred source of knowledge about vaccines. This agrees with the recently published data from other developed countries – Greece [24], Saudi Arabia [25], and the USA [26]. While online sources – such as social media or internet blogs – are gaining in popularity, educated medical professionals are still the most trusted sources of knowledge about health.
Conclusions
The research emphasized some important issues in the matter of the attitudes towards and knowledge about vaccines among surveyed Polish students. There were significant differences between various groups of students in their knowledge, attitude, source of information about vaccines, etc.
The results might indicate a substantial lack of education about vaccines and trust in healthcare workers’ knowledge among the students. This gap could be filled by the anti-vaccination movements’ propaganda which caused some hesitation in students in this matter and may contribute to the future failure of the nationwide vaccination program. We may also assume that public health attitudes and choices directly relate to education and knowledge levels.
Despite those possibilities, there is still a prospect that the medical community in Poland will prevent reluctance to vaccinate by the noticeable presence in social media – one of the most popular sources of information for young Poles. There is a need to overcome conspiracy theories about vaccines with reliable information based on scientific evidence from scientists and medical professionals.
It is also crucial to introduce courses devoted especially to vaccinology into university curriculums – particularly in medical faculties. Elements of this knowledge should also be included in science classes in compulsory primary and secondary education.
Disclosure
The authors report no conflict of interest.
References
1. Worboys M. Vaccines: conquering untreatable diseases. BMJ 2007; 334 (Suppl 1): s19.
2.
Health Resources & Services Administration. National vaccine injury compensation program data report. Available from: https:// www.hrsa.gov/vaccine-compensation/data (accessed: 1 March 2022).
3.
Rizwana A. Vaccines save lives, the circle composition, Volume 2, 2022. Available from: https://thecirclecomposition.org/vaccines/ (accessed: 1 March 2022).
4.
Public Health England. Diphtheria in England: 2020. Health Protection Report 2020; 15(7): 1-9. Available from: https://webcache.googleusercontent.com/search?q=cache:xPnL2UCugtUJ:https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1106302/diphtheria-guidelines-2022-v16.1-corrected.pdf&cd=2&hl=pl&ct=clnk&gl=pl (accessed: 1 March 2022).
5.
Gower CM, Scobie A, Fry NK, et al. The changing epidemiology of diphtheria in the United Kingdom, 2009 to 2017. Euro Surveill 2020; 25(11): 1900462.
6.
Strassburg MA. The global eradication of smallpox. Am J Infect Control 1982; 10(2): 53-59.
7.
Science Daily. How poxviruses such as smallpox evade the immune system. Available from: https://www.sciencedaily.com/releases/2008/01/080131122956.htm (accessed: 1 March 2022).
8.
Główny Urząd Statystyczny. Szczepienia ochronne dzieci i młodzieży [Central Statistical Office. Protective vaccinations for children and adolescents]. Available from: https://stat.gov.pl/obszary-tematyczne/zdrowie/zdrowie/szczepienia-ochronne- dzieci-i-mlodziezy,19,1.html (accessed: 1 March 2022).
9.
World Health Organization. Immunization coverage. Available from: https://www.who.int/news-room/fact-sheets/detail/immunization-coverage (accessed: 1 March 2022).
10.
Burki T. The online anti-vaccine movement in the age of COVID-19. Lancet Digit Health 2020; 2(10): e504-e505.
11.
Zucker JR, Rosen JB, Iwamoto M, et al. Consequences of under vaccination – measles outbreak, New York City, 2018-2019. N Engl J Med 2020; 382(11): 1009-1017.
12.
Sugerman DE, Barskey AE, Delea MG, et al. Measles outbreak in a highly vaccinated population, San Diego, 2008: role of the intentionally undervaccinated. Pediatrics 2010; 125(4): 747-755.
13.
Organisation for Economic Co-operation and Development. Revised field of science and technology (FOS) classification in the Frascati Manual. Available from: https://unstats.un.org/unsd/EconStatKB/KnowledgebaseArticle10269.aspx (accessed: 1 March 2022).
14.
The European higher education area. The Bologna Declaration of 19 June 1999. Available from: https://web.archive.org/web/ 20080211212119/http://www.bolognabergen2005.no/Docs/00-Main_doc/990719BOLOGNA_DECLARATION.PDF (accessed: 1 March 2022).
15.
Germani F, Biller-Andorno N. The anti-vaccination infodemic on social media: a behavioral analysis. PLoS One 2021; 16(3): e0247642.
16.
Betsch C, Renkewitz F, Betsch T, Ulshöfer C. The influence of vaccine-critical websites on perceiving vaccination risks. J Health Psychol 2010; 15(3): 446-455.
17.
Hussain A, Ali S, Ahmed M, Hussain S. The anti-vaccination movement: a regression in modern medicine. Cureus 2018; 10(7): e2919.
18.
Gołoś A, Lutyńska A. Thiomersal-containing vaccines – a review of the current state of knowledge. Przegl Epidemiol 2015; 69(1): 59-64, 157-161.
19.
Żuk P, Żuk P, Lisiewicz-Jakubaszko J. The anti-vaccine movement in Poland: the socio-cultural conditions of the opposition to vaccination and threats to public health. Vaccine 2019; 37(11): 1491-1494.
20.
Melovic B, Jaksic Stojanovic A, Vulic TB, et al. The impact of online media on parents’ attitudes toward vaccination of children-social marketing and public health. Int J Environ Res Public Health 2020; 17(16): 5816.
21.
Główny Inspektorat Sanitarny. ODRA [Chief Sanitary Inspectorate. Measles]. Available from: https://www.gov.pl/web/gis/odra (accessed: 1 March 2022).
22.
Kundi M, Obermeier P, Helfert S, et al. The impact of the parent-physician relationship on parental vaccine safety perceptions. Curr Drug Saf 2015; 10(1): 16-22.
23.
Davis TC, Fredrickson DD, Arnold CL, et al. Childhood vaccine risk/benefit communication in private practice office settings: a national survey. Pediatrics 2001; 107(2): E17.
24.
Simou E. Health information sources: trust and satisfaction. Int J Healthcare 2016; 2(1): 38-43.
25.
Alduraywish SA, Altamimi LA, Aldhuwayhi RA, et al. Sources of health information and their impacts on medical knowledge perception among the Saudi Arabian population: cross- sectional study. J Med Internet Res 2020; 22(3): e14414.
26.
Hesse BW, Nelson DE, Kreps GL, et al. Trust and sources of health information: the impact of the Internet and its implications for health care providers: findings from the first health information national trends survey. Arch Intern Med 2005; 165(22): 2618-2624.
