Target Population

The target population includes all children living in Social Vulnerability Index (SVI) zip codes of .6 or higher, as well as children living in lower SVI zip codes who are uninsured/underinsured, experiencing homelessness, and/or who are recently arrived immigrants or refugees without a medical home. Nearly all high SVI zip codes are in South King County.

Data reported each year by school districts showcases disparities in immunization rates. Among students in the three largest South King County school districts (Highline, Federal Way, and Kent), 86.6%, 87.3%, and 88.5% of students, respectively, were up-to-date on immunizations in 2022-23 (the most recent year for which data is available). This compares to an average of 91.4% across King County and 90.9% across the state of Washington. In comparably sized, higher-resourced school districts located in lower SVI zip codes of King County, such as Issaquah and Lake Washington, we see up-to-date rates that are significantly higher, at 94.6%.

We can also look more closely at individual vaccines to see a correlation between SVI and vaccination rates. For example, the highest SVI zip code in Seattle (98032) had 66.2% MMR vaccine coverage (2 doses) among 4-6 year olds in 2021. This compares to 78.6% coverage in the lowest SVI. These data suggest that children in higher-resourced areas are better protected from potential vaccine-preventable disease outbreaks, such as measles.

There are an estimated 103,920 school-aged children (ages 5-18) living in high SVI zip codes in King County. Our project vaccinated 2,942 children in 2022 and more than 4,085 children in 2023, for a total of more than 7,027 children vaccinated. However, we cannot provide a definitive estimate of the percentage of the population reached since we cannot say with absolute certainty that every child vaccinated lives in the same zip code where they attend school or attended a community event. Additionally, although the focus was school-aged children, some children ages 0-4 were vaccinated as well. Furthermore, the metric of "percentage of children vaccinated" is arguably not the most fitting indicator of success since many of the children our partners vaccinated represent populations that are among the hardest to reach due to language, transportation, poverty, housing, and other barriers. Our goal was not to vaccinate the greatest number of children possible, but rather to reach children who otherwise might not be vaccinated.

Addressing Health Inequities

This project is rooted in health equity, as demonstrated by multiple components, including:

Clinics were held in high SVI zip codes, thus reaching children with the greatest vulnerability to public health emergencies because of factors like socioeconomic status, household characteristics, racial and ethnic minority status, and housing and transportation. Clinics were, more rarely, held in lower SVI zip codes with an exclusive focus on children who are uninsured/underinsured, experiencing homelessness, and/or who are recently arrived immigrants or refugees without a medical home.
Clinics were held in a wide range of easily accessible locations and were hosted on evenings and weekends, allowing parents and caregivers to accompany their children outside of the typical workday. Both pre-registration and walk-in options were available. Additionally, some clinics were held at school during the school day and consents were obtained in advance, thus not requiring family members' presence. 
Interpretation was available at all clinics and key documents were translated.
Clinics were open to all children at no cost regardless of insurance status and immigration status.

Principles of health equity were included from the initial conceptualization of this program, and were explicitly stated in the RFA and communicated to our contractors as follows: 

Grounding Principles

Remove barriers that deter access: When planning vaccination events, partner with communities to identify barriers (such as distrust based on past practices, language access, transportation) and assets to tailor vaccination outreach and services to communities accordingly.
Create an inclusive process: Include people disproportionately impacted by vaccine-preventable diseases and other health issues, continuously and meaningfully. Incorporate these individuals and representatives of trusted community-based organizations that serve these communities in vaccine clinic planning, implementation, and after-action review processes.
Be intentionally anti-racist and accountable to Black, Brown, Indigenous, and People of Color communities: This means promoting a respectful and culturally appropriate approach to vaccine delivery where we respond to community needs and preferences, continuously learn and adjust based on what we hear from impacted communities, and publicly share data on race and ethnicity of people served in order to measure our progress toward providing meaningful access to marginalized communities.

Principles in Action

PHSKC requests that partners align with the following practices:

Focus on highest risk and most impacted: Use the CDC/ATSDR Social Vulnerability Index (SVI) database and maps to guide decision making around where to locate vaccination clinics. Select locations in zip codes with an SVI score of .6 or higher.
Work with community: Coordinate with community-based leaders and organizations with connections to highest risk communities and with particular focus on BIPOC communities. Ensure that communities help shape planning efforts from the outset.
Make registration easy: Allow walk-in vaccinations whenever feasible. If appointments are offered, ensure that appointment finding and registration systems are simple to use and easy to understand, available in most commonly spoken languages, and accessible for people with disabilities. Recognizing that any technology dependent system will create a digital barrier for many, where possible, offer personal assistance by phone.
Make vaccine available when and where people are available: Ensure appointment availability outside of regular business hours, including weekends and evenings. Work closely with schools and community- and faith-based organizations to inform clinic details.

Address transportation and mobility: Locate vaccination sites near public transportation. Ensure that sites are fully ADA compliant, have plain language and accessible signage, and are easy to navigate and comfortable for people of all abilities.
Ensure language access: From early planning, language access should be a priority, including the availability of in-person and/or phone interpreters. Consider the languages most spoken in the target geography and prioritize translation and interpretation for those languages.
Provide vaccination regardless of immigration status: Ensure that immigration status is not a barrier to vaccination.

How This Practice Is Innovative

While mobile vaccination clinics are by no means new to the field of public health, a few aspects of this program are arguably not conventional:

Contracting with trusted local healthcare partners to carry out clinics. This is a useful approach for health departments with limited overall staffing and/or minimal clinical staff. It allows LHD staff to focus time and attention on other endeavors rather than dedicating a large portion of staff time to mobile clinics. Additionally, healthcare providers may sometimes be better positioned to provide direct services to community members where mistrust of government is high, particularly in communities that have been previously harmed by government. Community members may be more receptive to non-governmental entities. 
Offering COVID-19 vaccine plus all routinely required vaccines throughout the calendar year. Mobile clinics frequently focus on a limited number of vaccines (e.g. COVID-19 and flu) and are most often held during back-to-school season and flu/respiratory virus season. By providing all routinely recommended childhood vaccines and hosting clinics throughout the year, this practice makes a variety of vaccines more accessible and maximizes opportunities to bring children up-to-date on all vaccinations.

PHSKC's Community Navigators buttress this practice by addressing vaccine confidence in high SVI areas of King County. Community Navigators are trusted messengers who address vaccine concerns and promote the benefits of vaccination through conversation and by using local and familiar communication platforms.

Creative Use of an Existing Tool

This practice is a creative use of the CDC/ATSDR Social Vulnerability Index (SVI). The SVI uses U.S. Census data to determine the social vulnerability of every census tract before, during, and after a hazardous event, such as an infectious disease outbreak. The SVI ranks each tract on 16 social factors, including poverty, lack of vehicle access, and crowded housing, and groups them into four related themes: socioeconomic status, household characteristics, racial and ethnic minority status, and housing type/transportation. Each tract receives a separate ranking for each of the four themes, as well as an overall ranking. SVI values range from 0 (least vulnerable) to 1 (most vulnerable).

By focusing on communities with higher SVI scores (0.6 or higher), this practice addresses disparities in vaccination coverage and prioritizes equitable access to childhood vaccinations. It demonstrates how local health departments can use SVI scores to consider socially vulnerable populations’ locations and strategically allocate mobile vaccination resources.

Evidence Base

Mobile vaccinations are a well-established approach for increasing access to vaccines. As FEMA states, "Mobile and pop-up sites bring vaccination centers closer to the communities and people that need them: they meet people where they work, live and socialize. They tackle the challenges that prevent people from receiving a vaccination: traveling distance, limited access to medical providers or vaccine centers, lack of mass transportation, mobility issues, work and family care schedules, (and) lack of vaccine confidence." 

The effectiveness of mobile vaccinations is backed up by numerous studies, such as a November 2023 Journal of Public Health study, "Mobile vaccination units substantially increase COVID-19 vaccinations: evidence from a randomized controlled trial." This study found that the vaccination rate in the sample of people offered mobile vaccinations surpassed the rate in those who only had traditional options available by a factor of 3.4 (+9.0 percentage points) over 3 weeks. The increase was present and highly statistically significant for women, men and for all age groups. The study also found no evidence that vaccination rates decreased at other locations where vaccines are offered, suggesting that mobile vaccinations reach more people overall, not just in a more expedient way.

This practice also builds on recommendations published by the Community Preventive Services Task Force (CPSTF) in their 2009 Finding and Rationale statement, "Increasing Appropriate Vaccination: Vaccination Programs in Schools and Organized Child Care Centers." The vaccination program included 27 studies of vaccination programs and provides strong evidence to support the effectiveness of on-site school and childcare center-located vaccination programs for improving vaccination rates and decreasing vaccine-preventable diseases. The Task Force found that such interventions can be less expensive than immunizations provided in healthcare settings because parents can avoid the loss of income associated with attending children’s clinic visits. It also demonstrated evidence of cost savings from school-based interventions due to increased vaccination rates, which the CPSTF notes reduce healthcare utilization, lifetime loss of productivity for children, and parental loss of productivity associated with care for the sick child. They note that offering vaccinations through schools and organized childcare centers can reduce the time spent by children and caregivers in obtaining recommended vaccinations, and it can supplement vaccination services delivered through healthcare systems, among other benefits.

Additionally, the CDC's March 26, 2021 MMWR concluded that the continued monitoring of vaccination coverage by social vulnerability metrics is critical for developing tailored, local vaccine administration and outreach efforts to reduce COVID-19 vaccination inequities.

Mobile Childhood Vaccination Clinics In High Social Vulnerability Index Zip Codes

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