Closing the immunisation gap: a tale of two cities
29 April 2026
Vaccination programmes have made remarkable progress, but coverage is still not evenly distributed across populations, leading to inequalities in health outcomes.
The people least likely to be vaccinated are typically those who already face the greatest health risks: people experiencing homelessness, substance dependence, mental illness, or some combination of all three. In this piece, HPP and Atlas Clarity LLC look at what two high-income cities, London and San Francisco, can teach us about reaching the people most likely to be left behind, and what it takes to get there.
Vaccination gaps are, above all, an equity issue
Coverage statistics can hide important insights. When public health agencies report that 80% or 90% of a population has been vaccinated, the headline obscures the question that matters most: who is in the remaining 10 or 20%? As England’s National Immunisation Programme Health Equity Audit makes clear, vaccine uptake is consistently lower among people with high deprivation; people from marginalised or minority groups; people with unstable housing, substance dependence or mental illness; and people with limited access to care. These groups face a convergence of barriers that map onto the five As of vaccine equity: access, affordability, awareness, acceptance and activation.
People who are not consistently included in GP registries are effectively invisible to public health monitoring and follow-up efforts, making them harder to reach and harder to count.
London: strong infrastructure, but persistent gaps, especially in routine coverage
Inequalities across London are well known. Someone born in one of London’s most deprived boroughs can expect to live 12 fewer healthy years than someone born in one of its wealthiest. Vaccination rates show similar disparities and again demonstrate the intersectionality of inequity. During the initial COVID-19 vaccination campaign, for example, only 46% of people who were homeless received one dose of the COVID-19 vaccine, and just 29% received a second – compared with approximately 75% uptake among the general adult population.
London’s core challenge is the mismatch between routine delivery channels and the realities of people living with mental illness, substance dependence and unstable housing. Compounding this is the persistent difficulty of low GP registration among these groups: people who are not consistently included in GP registries are effectively invisible to public health monitoring and follow-up efforts, making them harder to reach and harder to count.
San Francisco: high city-wide performance, but gaps remain in street-based populations
San Francisco is often held up as a vaccination success story. The San Francisco Department of Public Health describes the city as having ‘some of the highest sustained vaccination rates nationally’. The city also had one of the lowest COVID‑19 death rates in the US, with community collaboration and mobilisation credited for the success. These results are a testament to what is possible when public health, community organisations and political leadership align behind access.
But high overall coverage can mask sharp disparities in subpopulations. A 2024 peer‑reviewed study found that just over 72% of people who inject drugs in San Francisco had received the COVID-19 vaccine. On one hand, this is a strong result for a marginalised group; but on the other, it represents a major gap relative to the 95% uptake reported in the general population. The detail is even more instructive: people experiencing homelessness were half as likely to be vaccinated as those who were housed. Even within a highly resourced, pro‑vaccine city, the sharpest drop-off occurs precisely where substance dependence, unstable housing and mental illness converge.
San Francisco’s core challenge isn’t public appetite for vaccination. It’s sustaining the tailored, relationship‑based outreach needed to reach people living outside mainstream healthcare – especially younger people who inject drugs and those experiencing homelessness.
Even within a highly resourced, pro‑vaccine city, the sharpest drop-off occurs precisely where substance dependence, unstable housing and mental illness converge.
Building solutions around people’s needs: a San Francisco behavioural health community health centre
Westside Community Services is a behavioural health community health centre in San Francisco, which has been a pioneer of community-based mental health since it was established in 1967. Westside provides adult mental health services; methadone services; HIV/AIDS services; and child, youth, post-incarceration and family services at nine locations across the city. Originally founded to serve disenfranchised minority groups, Westside continues to serve the most underserved and underrepresented.
In addition to clinical and pharmacological behavioural health services, community outreach and case management, Westside also employs a psychosocial rehabilitation clubhouse model. The clubhouse model provides a supportive environment that focuses on recovery through work, peer relationships and social inclusion rather than traditional medical treatment. This unique approach helps individuals with serious mental illness and/or substance dependence alleviate isolation, foster self-assurance and build life skills.
Places such as the Westside Clubhouse provide an opportunity to address some of the five As of vaccine equity. The Clubhouse has programming three days a week and is co-located with a health centre, meaning members can receive clinical care and pick up medications at the same place they go to for community building.
Building off the success of pop-up clinics for COVID-19 immunisation, Atlas Clarity is partnering with Westside to host pop-up clinics for routine vaccinations such as influenza, pneumococcal and RSV. This partnership will enable Westside members to protect themselves against communicable diseases while addressing other aspects of their life, from social isolation and substance dependence to housing and employment status.
Lessons from both cities
London and San Francisco arrive at the same conclusion from different directions: high city-wide averages can conceal deep and persistent inequities, and the people most likely to be missed are those already facing the greatest disadvantage. Reaching them requires more than good intentions.
Programmes that work share common features. They go where people are, through mobile clinics, outreach teams, mental health services, hostels and drop-in centres. They operate with flexible hours and trusted partners. They remove administrative barriers – such as ID, GP registration, fixed appointments – that are manageable inconveniences for most people but insurmountable obstacles for some. They train staff in mental health and inclusion health. And they co-design their approaches with people who have lived experience of the barriers they are trying to dismantle, because services designed without that input tend to replicate the same exclusions.
Data matter too. Proactively identifying and following up with individuals who are absent from standard health registries is a logistical challenge, but one that is a prerequisite for equity. People who are invisible to data systems are invisible to public health efforts.
Vaccination remains a cornerstone of public health, but its foundation is only as strong as its reach into the most marginalised populations. The real measure of success of any vaccination programme isn’t how many people it reaches in total, but how effectively it reaches those whom the system has historically left behind. Closing the immunisation gap means not expecting people to navigate a system that wasn’t built for them, and instead building a system that meets them where they are.