Evidence gaps and challenges in maintaining and increasing vaccine uptake: A Delphi survey with Australian stakeholders.

ISSUE ADDRESSED: Increasing and maintaining vaccination uptake is crucial for preventing and managing infectious diseases. In the context of the post-coronavirus disease 2019 (COVID-19) pandemic landscape, this paper examines the perceptions of immunisation implementers and policymakers to uncover the challenges and evidence gaps in routine immunisation efforts. METHODS: We conducted an online two-round modified Delphi survey with immunisation experts, senior public servants, policymakers, policy advisory groups, and representatives from peak bodies from across Australia. We asked respondents to outline what they see as the greatest challenges to increasing and maintaining uptake of recommended vaccines in Australia; the most difficult aspects of their work in vaccination; the largest evidence gaps in vaccine uptake; and the kinds of social and behavioural research they would like to see prioritised. RESULTS: The two most important challenges for increasing and maintaining vaccine uptake were effectively communicating the benefits of vaccines to parents and the public and ensuring accessible and affordable vaccination services. Participants strongly agreed that 'communication about the importance of vaccination' was the most difficult aspect of their work. Consistently important was the need to better engage specific population groups, such as culturally and linguistically diverse people, pregnant people, at risk cohorts, and health care providers. Social and behavioural research about 'how to effectively address hesitancy' was ranked highly among participants. CONCLUSIONS: Findings from this project help provide an understanding of the behavioural, social, ethical, and policy knowledge needs for immunisation policy and implementation in Australia. To respond to vaccine challenges, increase coverage and build public trust in vaccination, policymakers and governments should incorporate social research into vaccination programmes. SO WHAT?: Australia is preparing to launch a Centre for Disease Control. This study demonstrates the importance of integrating social, behavioural, ethical, and policy research into the fabric of this new enterprise. It underlines the need to capacity-build a workforce able to deliver high-quality research in these areas, address the needs of immunisation implementers and policymakers, and achieve good outcomes for Australians.

The experience of traumatic events, psychological distress, and social support: links to COVID-19 vaccine hesitancy and trends with age in a group of older Australians.

BACKGROUND: Vaccination is important to reduce disease-associated morbidity and mortality in an ageing global population. While older adults are more likely than younger adults to accept vaccines, some remain hesitant. We sought to understand how traumatic events, psychological distress and social support contribute to older adults' intention to receive a COVID-19 vaccine and whether these experiences change with age. METHODS: We analysed survey data collected as part of the Sax Institute's 45 and Up Study in a population of Australian adults aged 60 years and over. Data were derived from the COVID Insights study; a series of supplementary surveys about how participants experienced the COVID-19 pandemic. RESULTS: Higher intention to receive a COVID-19 vaccine was associated with greater social support (adjusted odds ratio (aOR):1.08; 95%CI:1.06-1.11; p <.001) while lower intention was associated with personally experiencing a serious illness, injury or assault in the last 12 months (aOR:0.79; 95% CI:0.64-0.98; p =.03). Social support and the experience of traumatic events increased significantly with age, while psychological distress decreased. CONCLUSIONS: There may be factors beyond disease-associated risks that play a role in vaccine acceptance with age. Older Australians on the younger end of the age spectrum may have specific needs to address their hesitancy that may be overlooked.

Evaluating Pilot Implementation of 'PenCS Flu Topbar' App in Medical Practices to Improve National Immunisation Program-Funded Seasonal Influenza Vaccination in Central Queensland, Australia.

BACKGROUND: The 'PenCS Flu Topbar' app was deployed in Central Queensland (CQ), Australia, medical practices through a pilot programme in March 2021. METHODS: We evaluated the app's user experience and examined whether the introduction of 'PenCS Flu Topbar' in medical practices could improve the coverage of NIP-funded influenza vaccinations. We conducted a mixed-method study including a qualitative analysis of in-depth interviews with key end-users and a quantitative analysis of influenza vaccine administrative data. RESULTS: 'PenCS Flu Topbar' app users reported positive experiences identifying patients eligible for NIP-funded seasonal influenza vaccination. A total of 3606 NIP-funded influenza vaccinations was administered in the eight intervention practices, 14% higher than the eight control practices. NIP-funded vaccination coverage within practices was significantly higher in the intervention practices (31.2%) than in the control practices (27.3%) (absolute difference: 3.9%; 95% CI: 2.9%-5.0%; p < 0.001). The coverage was substantially higher in Aboriginal and Torres Strait Islander people aged more than 6 months, pregnant women and children aged 6 months to less than 5 years for the practices where the app was introduced when compared to control practices: incidence rate ratio (IRR) 2.4 (95% CI: 1.8-3.2), IRR 2.7 (95% CI: 1.8-4.2) and IRR 2.3 (1.8-2.9) times higher, respectively. CONCLUSIONS: Our evaluation indicated that the 'PenCS Flu Topbar' app is useful for identifying the patients eligible for NIP-funded influenza vaccination and is likely to increase NIP-funded influenza vaccine coverage in the eligible populations. Future impact evaluation including a greater number of practices and a wider geographical area is essential.

Childhood vaccine refusal and what to do about it: a systematic review of the ethical literature.

BACKGROUND: Parental refusal of routine childhood vaccination remains an ethically contested area. This systematic review sought to explore and characterise the normative arguments made about parental refusal of routine vaccination, with the aim of providing researchers, practitioners, and policymakers with a synthesis of current normative literature. METHODS: Nine databases covering health and ethics research were searched, and 121 publications identified for the period Jan 1998 to Mar 2022. For articles, source journals were categorised according to Australian Standard Field of Research codes, and normative content was analysed using a framework analytical approach. RESULTS: Most of the articles were published in biomedical journals (34%), bioethics journals (21%), and journals that carry both classifications (20%). Two central questions dominated the literature: (1) Whether vaccine refusal is justifiable (which we labelled 'refusal arguments'); and (2) Whether strategies for dealing with those who reject vaccines are justifiable ('response arguments'). Refusal arguments relied on principlism, religious frameworks, the rights and obligations of parents, the rights of children, the medico-legal best interests of the child standard, and the potential to cause harm to others. Response arguments were broadly divided into arguments about policy, arguments about how individual physicians should practice regarding vaccine rejectors, and both legal precedents and ethical arguments for vaccinating children against a parent's will. Policy arguments considered the normative significance of coercion, non-medical or conscientious objections, and possible reciprocal social efforts to offset vaccine refusal. Individual physician practice arguments covered nudging and coercive practices, patient dismissal, and the ethical and professional obligations of physicians. Most of the legal precedents discussed were from the American setting, with some from the United Kingdom. CONCLUSIONS: This review provides a comprehensive picture of the scope and substance of normative arguments about vaccine refusal and responses to vaccine refusal. It can serve as a platform for future research to extend the current normative literature, better understand the role of cultural context in normative judgements about vaccination, and more comprehensively translate the nuance of ethical arguments into practice and policy.

Communication Interventions and Assessment of Drivers for Hendra Virus Vaccination Uptake.

Hendra virus disease (HeVD) is an emerging zoonosis in Australia, resulting from the transmission of Hendra virus (HeV) to horses from Pteropus bats. Vaccine uptake for horses is low despite the high case fatality rate of HeVD in both horses and people. We reviewed evidence-based communication interventions to promote and improve HeV vaccine uptake for horses by horse owners and conducted a preliminary evaluation of potential drivers for HeV vaccine uptake using the Behavioural and Social Drivers of Vaccination (BeSD) framework developed by the World Health Organization. Six records were eligible for review following a comprehensive search and review strategy of peer-reviewed literature, but evidence-based communication interventions to promote and improve HeV vaccine uptake for horses were lacking. An evaluation of potential drivers for HeV vaccine uptake using the BeSD framework indicated that horse owners' perceptions, beliefs, social processes, and practical issues are similar to those experienced by parents making decisions about childhood vaccines, although the overall motivation to vaccinate is lower amongst horse owners. Some aspects of HeV vaccine uptake are not accounted for in the BeSD framework (for example, alternative mitigation strategies such as covered feeding stations or the zoonotic risk of HeV). Overall, problems associated with HeV vaccine uptake appear well-documented. We, therefore, propose to move from a problems-focused to a solutions-focused approach to reduce the risk of HeV for humans and horses. Following our findings, we suggest that the BeSD framework could be modified and used to develop and evaluate communication interventions to promote and improve HeV vaccine uptake by horse owners, which could have a global application to promote vaccine uptake for other zoonotic diseases in animals, such as rabies.

Association between traumatic life events and vaccine hesitancy: A cross-sectional Australian study.

OBJECTIVES: We sought to identify associations between the experience of traumatic life events and vaccination intention to inform whether trauma-affected individuals require targeted interventions when addressing vaccine hesitancy. STUDY DESIGN: We conducted an online cross-sectional survey to identify whether direct or indirect exposure to various traumatic life events and the presence of post-traumatic stress disorder (PTSD) symptoms are associated with willingness to receive a COVID-19 vaccine in an Australian sample. METHODS: A national online questionnaire was administered to a representative sample of 1050 Australian adults in September 2021. RESULTS: Lower willingness to receive a COVID-19 vaccine was associated with direct experience of a fire or explosion (adjusted odds ratio [aOR]: 0.42; 95% confidence interval [CI]: 0.23-0.78; P = 0.006), direct experience of severe human suffering (aOR:0.39; 95% CI: 0.21-0.71; P = 0.002) and screening positive for PTSD symptoms (aOR:0.52; 95% CI: 0.33-0.82; P = 0.005). Conversely, higher willingness to receive a COVID-19 vaccine was associated with indirect exposure to severe human suffering (aOR: 2.0; 95% CI: 1.21-3.22; P = 0.007). CONCLUSIONS: Our findings suggest that the experience of traumatic events and the presence of PTSD symptoms can contribute to vaccination decisions. Our work adds to the growing recognition of the need to effectively mediate the influence of traumatic experiences on encounters within the medical setting and supports the importance of addressing the needs of trauma-affected individuals in their vaccination experiences.

COVID-19 testing decisions and behaviours in two Australian cities.

ISSUE ADDRESSED: High levels of testing are crucial for minimising the spread of COVID-19. The aim of this study is to investigate what prevents people from getting a COVID-19 test when they are experiencing respiratory symptoms. METHODS: Semi-structured, qualitative interviews were conducted with 14 purposively sampled adults between 20 November 2020 and 3 March 2021 in two capital cities of Australia and analysed thematically. The analysis included people who reported having respiratory symptoms but who did not undergo a COVID-19 test. RESULTS: Participants appraised risks of having COVID-19, of infecting others or being infected whilst attending a testing site. They often weighed these appraisals against practical considerations of knowing where and how to get tested, inconvenience or financial loss. CONCLUSIONS: Clear public health messages communicating the importance of testing, even when symptoms are minor, may improve testing rates. Increasing the accessibility of testing centres, such as having them at transport hubs is important, as is providing adequate information about testing locations and queue lengths. SO WHAT?: The findings of our study suggest that more needs to be done to encourage people to get tested for COVID-19, especially when symptoms are minor. Clear communication about the importance of testing, along with easily accessible testing clinics, and financial support for those concerned about financial impacts may improve testing rates.

COVID-19 vaccine acceptance among pregnant women and the reasons for hesitancy: A multi-centre cross-sectional survey.

BACKGROUND: On 9 June 2021, the Australian Technical Advisory Group on Immunisation and Royal Australian and New Zealand College of Obstetricians and Gynaecologists recommended that pregnant women receive Comirnaty (Pfizer) messenger RNA vaccine at any stage of pregnancy. AIM: This multi-centre study aimed to assess vaccine acceptance, reasons for hesitancy and determine if differences exist between health districts, to inform future policy strategies for COVID-19 vaccination in pregnancy. MATERIALS AND METHODS: An online survey (developed based on the World Health Organization Behavioural and Social Drivers survey and modified for the pregnant population) was administered to a sample population of pregnant women attending antenatal clinics at two metropolitan hospitals (Westmead and Royal North Shore Hospital (RNSH)) in New South Wales between 15 September 2021 and 22 October 2021. RESULTS: There were 287 pregnant women surveyed (Westmead 198 (69%), RNSH 66 (23%), no site 23 (8%)). There was a significantly lower Socio-Economic Indexes for Areas score (5.66 vs 9.45, P = 0.001), fewer women born in Australia (37% vs 53%, P = 0.02) and higher number of children (0.77 vs 0.41, P = 0.01) among Westmead respondents. There was lower vaccination uptake (68% vs 86%, P = 0.01) and willingness to receive vaccine (68% vs 88% P = 0.01) at Westmead compared to RNSH. There was an increased proportion of respondents who were concerned that the vaccine could cause harm to the unborn baby at Westmead (38% vs 11%, P = 0.01). CONCLUSIONS: Along with healthcare provider recommendation for vaccination in pregnancy, materials should be targeted to specific safety concerns of pregnant women.

Willingness to receive a vaccine is influenced by adverse events following immunisation experienced by others.

An adverse event following immunization (AEFI) can have consequences for an individual's future decision making and may contribute to vaccine hesitancy. AEFIs vary in severity and can be experienced directly (by an individual themselves) or indirectly (through witnessed or recounted events). We sought to measure the prevalence of specific AEFIs and understand which AEFIs have the greatest associations with reduced willingness to receive a vaccine and how injection anxiety may moderate the relationship. We conducted a cross-sectional online survey with both qualitative and quantitative elements in a sample of adults aged 18 years and over in Australia. Nineteen percent of the 1050 respondents reported experiencing an AEFI that they found stressful. Those who experienced an AEFI reported significantly higher levels of injection anxiety than those who did not. Within the group who reported experiencing an AEFI, respondents were significantly less likely to be willing to receive a COVID-19 vaccine if they reported: indirect exposure to an uncommon/rare AEFI compared with other AEFIs (aOR:0.39; 95% CI: 0.18-0.87); indirect exposure to a scientifically unsupported AEFI compared with other AEFIs (aOR:0.18; 95% CI: 0.05-0.57). Direct exposure to an AEFI was not associated with willingness to receive a COVID-19 vaccine. For those who reported experiencing an AEFI, the odds of willingness to receive a COVID-19 vaccine decreased significantly with an increase in injection anxiety (aOR:0.94; 95% CI: 0.9-0.98). Our results suggest that more is needed to mitigate the consequences of AEFIs on vaccine willingness. Empathically acknowledging at a community level, the experience of both real and perceived AEFIs and incorporating accounts of positive vaccination experiences in vaccine hesitancy interventions may be useful.

Traumatic Events and Vaccination Decisions: A Systematic Review.

Despite the apparent relationship between past experiences and subsequent vaccination decisions, the role of traumatic events has been overlooked when understanding vaccination intention and behaviour. We conducted a systematic review to synthesize what is known about the relationship between traumatic events and subsequent vaccination decisions. MEDLINE, PsycINFO and CINHAL electronic databases were searched, and 1551 articles were screened for eligibility. Of the 52 articles included in full-text assessment, five met the eligibility criteria. Findings suggest that the experience of trauma is associated with individual vaccination decisions. Social and practical factors related to both trauma and vaccination may mediate this relationship. As this is a relatively new field of inquiry, future research may help to clarify the nuances of the relationship. This review finds that the experience of psychological trauma is associated with vaccination intention and behaviour and points to the potential importance of a trauma-informed approach to vaccination interventions during the current global effort to achieve high COVID-19 vaccine coverage.

Qualitative assessment of caregiver experiences when navigating childhood immunisation in urban communities in Sierra Leone.

OBJECTIVE: To gain in-depth understanding of the caregiver experience when navigating urban immunisation services for their children. DESIGN: An exploratory qualitative assessment comprising 16 in-depth interviews using an interpretative phenomenology approach. SETTING: Caregivers were purposively recruited from slums (n=8) and other urban communities (n=8) in the capital city of Sierra Leone. PARTICIPANTS: Caregivers of children ages 6-36 months old who were fully vaccinated (n=8) or undervaccinated (n=8). RESULTS: Emotional enablers of vaccination were evident in caregivers' sense of parental obligation to their children while also anticipating reciprocal benefits in children's ability to take care of their parents later in life. Practical enablers were found in the diversity of immunisation reminders, information access, information trust, getting fathers more involved, positive experiences with health workers and postvaccination information sharing in the community. Underlying barriers to childhood vaccination were due to practical constraints such as overcrowding and long waiting times at the clinic, feeling disrespected by health workers, expecting to give money to health workers for free services and fear of serious vaccine side effects. To improve vaccination outcomes, caregivers desired more convenient and positive clinic experiences and deeper community engagement. CONCLUSIONS: Health system interventions, community engagement and vaccination outreach need to be tailored for urban settings. Vaccine communication efforts may resonate more strongly with caregivers when vaccination is framed both around parental responsibilities to do the right thing for the child and the future benefits to the parent.

"Scary to get, more scary not to": COVID-19 vaccine acceptance among healthcare workers in Central Queensland, Australia, a cross-sectional survey.

Background: Behavioural and social drivers (BeSD) of coronavirus disease 2019 (COVID-19) vaccine acceptance among Australian healthcare workers (HCW) living and working in regional areas are not well studied. Understanding local HCWs' COVID-19 risk perceptions and potential barriers to COVID-19 vaccine uptake is crucial in supporting rollout. We aimed to understand the COVID-19 vaccine drivers among HCW in Central Queensland (CQ), Australia. Method: A cross-sectional online survey of HCWs in CQ between 17 May and 31 May 2021, based on the BeSD framework adapted from the World Health Organization (WHO) Data for Action guidance, consisting of the five instrument domains: what people think and feel; social processes; motivations; practical issues; and vaccination uptake. Results: Of the 240 responding HCWs within Central Queensland Hospital and Health Service, 78% were female. Of the participating HCWs, 64% percent had received at least one dose of a COVID-19 vaccine; of those who had not yet received a vaccine, 53% said they were willing to receive one. Factors associated with vaccine acceptance included: belief that the vaccine was important for their health (81%; odds ratio (OR): 7.2; 95% confidence interval (CI): 3.5-15.5); belief that their family and friends wanted them to have the vaccine (64%; OR: 6.7; 95% CI: 2.9-16.7); trust in the vaccine (72%; OR: 6.4; 95% CI: 3.5-12.0); and confidence in being able to answer patients' questions about the vaccine (99%). Conclusions: These findings suggest that a combination of communications and educational material framed around the benefits and social norms of vaccination, along with materials addressing vaccine safety concerns, will encourage HCW to take up a COVID-19 vaccine.

'Get your own house in order': Qualitative dialogue groups with nonvaccinating parents on how measles outbreaks in their community should be managed.

OBJECTIVE: Communities with high levels of vaccine rejection present unique challenges to vaccine-preventable disease outbreak management. We sought perspectives of nonvaccinating parents to inform public health responses in such communities. METHODS: Nineteen purposively sampled nonvaccinating Australian parents participated in one of seven online dialogue groups. We asked what they thought parents, school principals and public health professionals should do in a hypothetical school measles outbreak and used a framework approach to data analysis. RESULTS: Parents' views were grounded in strong beliefs in parental responsibility and the belief that vaccines are not effective, thus unvaccinated children do not therefore pose a threat. They then reasoned that the forced exclusion of unvaccinated children from school in a measles outbreak was disproportionate to the risk they pose, and their child's right to education should not be overridden. Nonvaccinating parents judged that all parents should keep sick children at home regardless of disease or vaccination status; that school principals should communicate directly with parents and avoid using social media; that public health professionals should provide information to parents so they can decide for themselves about excluding their children from school; that public health responses should avoid accidental identification of unvaccinated children and that mainstream media should be avoided as a communication tool. CONCLUSION: Nonvaccinating parents do not always agree with current Australian approaches to measles outbreak management. Their perspectives can inform approaches to outbreak responses in communities with high levels of vaccine rejection. PATIENT OR PUBLIC CONTRIBUTION: We sought input from individuals who did and did not vaccinate on study design in its early phases. Individual conversations were used deliberately as we felt the group advisory situation may have felt less safe for nonvaccinating parents, given the divisive and often hostile nature of the topic.

COVID-19 and missed or delayed vaccination in 26 middle- and high-income countries: An observational survey.

BACKGROUND: The COVID-19 pandemic has disrupted vaccination services and raised the risk of a global resurgence of preventable diseases. We assessed the extent of and reasons for missed or delayed vaccinations (hereafter 'missed') in middle- and high-income countries in the early months of the pandemic. METHODS: From May to June 2020, participants completed an online survey on missed vaccination. Analyses separated missed childhood and adult vaccination in middle-and high-income countries. RESULTS: Respondents were 28,429 adults from 26 middle- and high-income countries. Overall, 9% of households had missed a vaccine, and 13% were unsure. More households in middle- than high-income countries reported missed childhood vaccination (7.6% vs. 3.0%) and missed adult vaccination (9.6% vs. 3.4%, both p < .05). Correlates of missed childhood vaccination in middle-income countries included COVID-19 risk factors (respiratory and cardiovascular diseases), younger age, male sex, employment, psychological distress, larger household size, and more children. In high-income countries, correlates of missed childhood vaccination also included immunosuppressive conditions, but did not include sex or household size. Fewer correlates were associated with missed adult vaccination other than COVID-19 risk factors and psychological distress. Common reasons for missed vaccinations were worry about getting COVID-19 at the vaccination clinic (15%) or when leaving the house (11%). Other reasons included no healthcare provider recommendation, clinic closure, and wanting to save services for others. INTERPRETATION: Missed vaccination was common and more prevalent in middle- than high-income countries. Missed vaccination could be mitigated by emphasizing COVID-19 safety measures in vaccination clinics, ensuring free and accessible immunization, and clear healthcare provider recommendations.

Labels matter: Use and non-use of 'anti-vax' framing in Australian media discourse 2008-2018.

Childhood vaccine refusal is a globally contentious topic, with some jurisdictions addressing it with punitive policies. Media discourse influences how solutions are framed by implying blame - a process known as framing. We examined Australian media discourse on vaccine rejection over a period in which mandatory childhood vaccination policies were discussed and introduced, focusing on the common Australian pejorative term 'anti-vaxxer'. We mapped frequency of use from January 2008 to December 2018. We then searched Factiva for print media articles on childhood vaccination and parents published in that period, searching separately for articles using and not using 'anti-vaxxer' and variants. We constructed a set of 85 articles that did, and 85 articles date-matched that did not use the term to make comparisons and conducted a frame analysis of each set. 'Anti-vaxxer' was absent in Australian media discourse 2008-2010, rising to a peak of 247 articles using the term at the height of legislative change in 2017. Parents were framed as: 1) deviant "others"; 2) ignorant and in need of informing; 3) vulnerable and in need of protection from anti-vaccination activists; 4) thoughtful, critical, informed, and in need of agency and respect; 5) entitled, privileged and selfish; and finally, 6) lacking access to vaccination, rather than being unwilling. Articles using 'anti-vax' terms were more likely to negatively characterise non-vaccinating parents, while articles not including this language were more likely to frame them as thoughtful or lacking access. This study clearly demonstrates strategic use of pejoratives in the Australian mass media around a time of pressure for legislative change and conflation of anti-vaccination activists with non-vaccinating parents. We suggest fundamental changes to how non-vaccination is framed and dealt with in the media to curb polarization and fostering more respectful dialogue, and better social and public health outcomes.

Stigmatized for standing up for my child: A qualitative study of non-vaccinating parents in Australia.

BACKGROUND: Vaccine refusal is highly polarizing in Australia, producing a challenging social landscape for non-vaccinating parents. We sought to understand the lived experience of non-vaccinating parents in contemporary Australia. METHODS: We recruited a national sample of non-vaccinating parents of children <18 yrs, advertising on national radio, in playgrounds in low vaccination areas, and using snowballing. Grounded Theory methodology guided data collection (via semi-structured interviews). Inductive analysis identified stigmatization as a central concept; stigma theory was adopted as an analytical lens. RESULTS: Twenty-one parents from regional and urban locations in five states were interviewed. Parent's described experiences point to systematic stigmatization which can be characterized using Link & Phelan's five-step process. Parents experienced (1) labelling and (2) stereotyping, with many not identifying with the "anti-vaxxers" portrayed in the media and describing frustration at being labelled as such, believing they were defending their child from harm. Participants described (3) social "othering", leading to relationship loss and social isolation, and (4) status loss and discrimination, feeling "brushed off" as incompetent parents and discriminated against by medical professionals and other parents. Finally, (5) legislative changes exerted power over their circumstances, rendering them unable to provide their children with the same financial and educational opportunities as vaccinated children, often increasing their steadfastness in refusing vaccination. CONCLUSION: Non-vaccinating Australian parents feel stigmatized for defending their child from perceived risk of harm, reporting a range of social and psychological effects, as well as financial effects from policies which disadvantaged their children through differential financial treatment, and diminished early childhood educational opportunities. While it might be argued that social stigma and exclusionary policies directed a small minority for the greater good are justified, other more nuanced approaches based on better understandings of vaccine rejection could achieve comparable public health outcomes without the detrimental effect on unvaccinated families.