Introduction

The United States (US) recorded over 2,200 measles cases in 2025, constituting the highest number of cases since measles was declared eliminated in 2000 [1,2]. This resurgence follows several years of small declines in coverage for measles, mumps, and rubella (MMR) vaccination. Among children enrolled in kindergarten, coverage dropped from the Healthy People 2030 goal of 95% during the 2019–2020 school year to 93% during 2024–2025 [1,3]. This coverage is characterized by pronounced geographic disparities, ranging from 98% in Connecticut to just 80% in Idaho, with fewer than one-quarter of states meeting the 95% threshold needed to maintain community immunity [3,4]. While measles is perhaps the most dramatic example, kindergarten coverage for other childhood vaccines, including diphtheria, tetanus, and acellular pertussis (DTaP), polio, and varicella, have seen similar declines, from 95% to 92–93%, over the past five school years [3,4]. There is also concern for adolescent vaccines as HPV vaccination coverage stagnated for the third year in 2024, with only 63% of 13- to 17-year-olds up to date on the multi-dose series [5].

Taken together, these data suggest that renewed attention to childhood vaccination coverage is urgently needed to reverse these concerning trends. A promising direction is engagement of social networks with the broad reach needed to address the national scope of the problem across multiple vaccine types [6]. Primary care providers have long served as champions for routine childhood vaccination, but investment in other trusted messengers may be valuable in light of post-pandemic declines in trust of physicians and healthcare organizations [7–10].

Engaging parent advocates and their social networks may offer another way to increase coverage for MMR and other routine childhood vaccines. Parents have the potential to advocate for vaccination by sharing resources, social media posts, and personal stories, having conversations with other parents, and leading community campaigns [11–14]. On the one hand, prior research suggests that encouragement from family members, friends, and social networks is a predictor of vaccine acceptance, and over 80% of parents trust these peers for vaccine-related advice [11,15,16]. For example, parents report improved vaccine-related attitudes after engaging in conversations promoting vaccination with parent advocates, and social network analysis suggests such “people networks” predict parents’ own vaccination behavior [11,15]. On the other hand, parents may also discourage vaccination given their own beliefs, attitudes, and experiences [17]. For example, even among parents who receive a provider recommendation, HPV vaccine refusal is higher for those exposed to anti-HPV vaccination advice from social contacts, suggesting that parents’ influence cuts both ways through encouraging or discouraging vaccination [15,16]. To our knowledge, no prior nationally representative studies have compared these advocacy behaviors to understand how common they are or what they entail.

We sought to address this gap by examining parents’ role in advocating for and against routine childhood vaccines. Our study aim was to evaluate the prevalence and correlates of encouraging or discouraging childhood vaccination to other parents. We also sought to compare encouragers and discouragers on the vaccine types, audiences, strategies, and modes they engaged, as well as on the advocacy identities they endorsed. In this way, our study seeks to advance opportunities to engage parent advocates in future efforts to increase vaccination coverage.

Methods

Results

Sample characteristics

Participants were mothers (56%), fathers (43%), or other guardians (1%, Table 1). Most identified as non-Hispanic White (55%), Hispanic (23%), or non-Hispanic Black (12%). More than one-third of parents had a bachelor’s degree or more education (42%). Political leaning was split across conservative (34%), moderate (43%), and liberal (23%) views. Household income ranged from low (<$50,000, 19%) to medium ($50,000-$99,999, 25%) to high (≥$100,000, 56%). Over one-third of participants lived in the South (40%), with the remainder in the West (23%), Midwest (21%), or Northeast (16%). Over one-half of parents reported high vaccination confidence (57%).

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Table 1. Sample characteristics (n = 1,315).

https://doi.org/10.1371/journal.pone.0354147.t001

Correlates of vaccine advocacy

Fathers and other guardians were less often vaccine encouragers compared to mothers (32% vs. 39%, p < .05, Table 2). Parents with moderate and liberal versus conservative political leanings were more often encouragers (38% and 50% vs. 24%, p < .05), as were parents with high versus low vaccination confidence (48% vs. 20%, p < .05). These multivariable findings mirrored those of bivariate analyses (S1 Table).

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Table 2. Multivariable correlates of vaccine encouraging and discouraging (n = 1,315).

https://doi.org/10.1371/journal.pone.0354147.t002

Non-Hispanic Black parents were more often vaccine discouragers compared to non-Hispanic White parents (20% vs. 10%, p < .05, Table 2). Parents with high versus low vaccination confidence were less often discouragers (6% vs. 20%, p < .05). In bivariate analyses, vaccine discouraging was also associated with lower educational attainment, conservative versus liberal political leaning, and lower household income, yet these associations did not retain statistical significance in multivariable analyses (S1 Table).

Vaccine advocacy role

Vaccine types.

Higher proportions of vaccine encouragers (n = 463) than discouragers (n = 144) focused their advocacy on measles or MMR (50% vs. 10%) and meningitis vaccines (31% vs. 10%, both p < .05, Fig 1). In contrast, more discouragers than encouragers focused on Covid-19 vaccine (53% vs. 28%, p < .05). Encouragers and discouragers similarly focused on seasonal flu (44% and 41%), HPV (31% and 32%), and all routine vaccines for children (21% and 21%).

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Fig 1. Routine vaccines parent advocates reported encouraging or discouraging to other parents.

Reported as percentage of parents who encouraged or discouraged each vaccine type.

https://doi.org/10.1371/journal.pone.0354147.g001

Audiences.

Both vaccine encouragers (n = 477) and discouragers (n = 149) most often reported that audiences for their advocacy included close friends (58% vs. 41%) and family members (57% vs. 42%), although encouragers reported engaging these audiences more often than discouragers (both p < .05, Table 3). Other audiences that encouragers and discouragers reported engaging were parents in their child’s school or community (27% and 22%), parents on social media (12% and 12%), and the broader public (7% and 13%).

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Table 3. Audiences, strategies, and modes among parents who reported vaccine encouraging (n = 477) and discouraging (n = 151).

https://doi.org/10.1371/journal.pone.0354147.t003

Strategies.

Higher proportions of vaccine encouragers (n = 472) than discouragers (n = 151) reported using the advocacy strategies of sharing their own experiences getting vaccines for children (47% vs. 27%) and information about which providers to go to (13% vs. 5%, both p < .05, Table 3). In contrast, more discouragers than encouragers shared websites or other resources (31% vs. 20%, p < .05). Encouragers and discouragers similarly reported sharing information about vaccine effectiveness (38% and 42%) and safety (33% and 35%), as well as their own advice or opinions about vaccines (35% and 36%).

Modes.

More vaccine encouragers (n = 476) than discouragers (n = 149) reported using conversations with other parents as an advocacy mode (67% vs. 42%, p < .05, Table 3). In contrast, more discouragers than encouragers used state or national advocacy (8% vs. 4%, p < .05). Encouragers and discouragers similarly used social media posts (17% and 23%) and school or community advocacy (8% and 15%).

Advocacy identities

Parents who reported only encouraging vaccines (n = 399) most often endorsed the identities of vaccine advocate (43%), child health advocate (28%), and wellness advocate (24%, Table 4). These identities were also most common among parents who reported both encouraging and discouraging vaccines (n = 77) or neither behavior (n = 760): vaccine advocate (20% and 18%, respectively), child health advocate (18% and 18%), and wellness advocate (19% and 20%). In contrast, parents who reported only discouraging vaccines (n = 73) most often endorsed the identities of vaccine skeptic (45%), medical freedom activist (22%), and anti-vaccine activist (22%), in addition to child health advocate (23%).

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Table 4. Vaccine advocacy identities endorsed by parents who only encourage other parents to vaccinate (n = 399), only discourage other parents (n = 73), both encourage or discourage (n = 77), or neither (n = 760).

https://doi.org/10.1371/journal.pone.0354147.t004

Discussion

Over a third of US parents in our nationally representative study reported advocating for other parents to vaccinate their children, while only about one in ten discouraged other parents from vaccinating. Importantly, vaccine encouragers most often focused on measles vaccine while discouragers seldom did so, suggesting a potential asymmetry in the advocacy landscape favorable to public health during the recent measles resurgence. Overall, the two groups reported similar audiences, strategies, and modes, with encouragers especially likely to focus on family and friends, engage in conversations, and share vaccine experiences. Taken together, our findings suggest that vaccine encouragers deserve more attention than they typically receive, including as promising partners in efforts to increase coverage of MMR and other routine childhood vaccinations.

Our study highlights several understudied aspects of vaccine advocacy that can inform efforts to engage parents in vaccine promotion efforts. First, vaccine encouragers were far more common than discouragers, which has not to our knowledge been previously quantified. Indeed, extrapolating our findings to the US population suggests that there could be about ten million vaccine encouragers among parents of children ages 9–12 alone, which constitutes a large pool of potential partners [32]. Second, vaccine encouragers were relatively well represented across subgroups of parents, including by race/ethnicity and household income. Vaccination confidence emerged as the strongest correlate of encouraging vaccination, suggesting that parents’ vaccination beliefs may be more important than demographics for identifying supporters of routine childhood vaccination. Finally, vaccine encouragers often reported advocating at the interpersonal level by engaging friends and family. Prior research suggests that this type of peer-to-peer communication may be especially influential in informing parents’ vaccination behaviors [11,15,16]. In sum, our findings indicate that vaccine encouragers constitute a potential advocacy resource due to their large numbers, broad distribution, and integration into interpersonal social networks where their voices may be especially influential.

Our study also provides valuable data on parents who discourage vaccination and suggests a degree of nuance in advocacy behaviors. First and most notably, we were surprised to find that about half of vaccine discouragers also reported vaccine encouraging. This finding undercuts the common framing of advocates as entirely for or against vaccination and deserves additional research. Second, we observed relatively few discouragers. While this finding is reassuring, it is important to keep in mind that such parents can still be highly influential, especially to the extent they share negative vaccine information, which prior research shows can be more memorable and compelling than positive information [21]. Third, we found discouragers most often shared vaccine effectiveness and safety information and their own advice and opinions, but less often shared vaccine experiences compared to encouragers. Discouragers also more often engaged in state and national advocacy and less often had conversations with other parents, suggesting discouragers may be drawn to a larger anti-vaccine movement rather than engaging with their own social contacts. Thus, our study provides a new perspective for understanding how discouragers engage with other parents and the broader public, while also suggesting the need to move beyond conceptualizing advocacy as purely pro- versus anti-vaccination.

Relatedly, less than half of parents in our sample endorsed any of the prespecified identity terms we offered, suggesting parents may not readily adopt vaccine-related labels often used in the popular press and social media, even when they report advocacy behaviors. Prior research on group identities among pro- and anti-vaccination supporters suggests encouragers may have stronger overall identity endorsements compared to discouragers [33–35], but our results call into question how useful advocacy terms are for public health practitioners. Perhaps not surprisingly, vaccine advocate was the most commonly endorsed term among encouragers, and vaccine skeptic, medical freedom activist, and anti-vaccine activist were most common among discouragers. Yet, endorsement for more general terms including child health advocate and wellness advocate was consistent across advocacy behaviors, suggesting that those identities resonate with parents who both encourage and discourage vaccines. Given the lack of strong affinity for identity terms, efforts to categorize parents as pro- versus anti-vaccination when developing interventions should consider a degree of variation to avoid overly defining such groups. In terms of public health practice, it may be more effective to focus on the advocacy behavior of encouraging vaccines, rather than labeling parents with specific identity terms. In doing so, we can build on longstanding efforts to engage “fence sitters” and question our society’s trend towards polarizing vaccine beliefs [36].

Our findings suggest several avenues for engaging parents in interventions to increase coverage of MMR and other routine childhood vaccinations. Parents may need additional support to shift from interpersonal conversations with family and friends to broader advocacy as their mode, as encouragers were less likely to engage in state or national advocacy compared to discouragers. For example, efforts could leverage resources such as Vaccinate Your Family’s no-cost educational resource that teaches parents the basics of vaccine communication and safety and Voices for Vaccines’ “Vax Ambassadors” program which provides training sessions on advocacy-related topics and tools [37,38]. In light of our findings, public health leaders should consider ways to support these organizations in making vaccine advocacy opportunities more accessible for parents. We can also gain insight from previous research in the state of Washington that trained parent advocates who value immunization to engage in positive dialogue in their communities. The “Immunity Community” increased parents’ vaccine-related knowledge, vaccination confidence, and concern about other parents not vaccinating their children post-intervention [11]. While parents in our study similarly shared vaccine information and resources through conversations, those in the “Immunity Community” study also posted on social media and organized community-wide events to improve vaccine-related attitudes [11]. Given ongoing outbreaks of measles and other vaccine-preventable diseases, the time may be ripe to further promote social media use and organizing among parent advocates.

Our study also suggests several implications for future research. Vaccine encouragers may be conceptualized as an implementation strategy similar to clinical champions, or healthcare professionals who help their colleagues improve the delivery of evidence-based care in clinical settings [39]. As an opportunity for possible collaboration, clinics and parent-based organizations could consider pairing clinical champions with parents who might work together to improve interpersonal vaccine communication, with a specific focus on measles vaccination given the current outbreaks. Future research can also further support intervention studies through the development of validated measures to assess advocacy, building on a recently developed scale assessing advocacy behaviors for childhood vaccines among adults [40]. Lastly, future research should explore why parents might not report advocacy behavior including potential barriers such as lack of time and adequate resources or viewing vaccination as a provider’s responsibility to discuss, rather than parents’ themselves.

Our study has several strengths, including a large, nationally representative sample of parents that includes variation across key demographics, including parenting role, race/ethnicity, and political leaning. Limitations include the cross-sectional study design and use of self-reported data on vaccine advocacy behaviors. We acknowledge that we cannot determine causality in observed associations, such as those between vaccination confidence and advocacy behavior. Social desirability may have led some participants to overstate their involvement in vaccine encouraging or underreport discouraging, potentially inflating our encourager to discourager ratio. In addition, the terms “encouraging” or “discouraging” vaccines are not previously validated. While cognitive interviews of our survey items confirmed a common understanding, parents may have had differing interpretation of vaccine advocacy behavior depth or intensity. Given that our survey was fielded in May 2025, we characterized parental vaccine advocacy after the Covid-19 pandemic and during the start of a new government administration. Our findings should be considered in light of recent drops in public health trust, reduction of vaccine-related infrastructure, and highly publicized vaccine-preventable diseases which may have influenced the frequency of vaccine encouraging and discouraging compared to prior years [41–43]. Future studies may benefit from specifying a time frame for vaccine advocacy behaviors, as well as collecting data on additional variables, such as prior vaccination behavior and medical mistrust, to further assess potential correlates and confounders. Finally, our findings may be most generalizable to parents of children ages 9–12 years, as parents of younger or older children may have different advocacy priorities based on their child’s recommended vaccine schedule.

Supporting information