Respiratory syncytial virus (RSV) is a familiar seasonal illness, but the tools to prevent it are new. Canada has recently approved vaccines for older adults and pregnant people, along with a long-acting monoclonal antibody that can protect infants through their first RSV season.These innovations offer new ways to reduce hospitalizations and severe illness. Yet whether Canadians can access them still depends largely on where they live.Across the country, provincial RSV programs vary widely in eligibility, scope and public funding — see, for example, Ontario RSV program updates and Alberta immunization program information. Read more: RSV FAQ: What is RSV? Who is at risk? When should I seek emergency care for my child? An infant eligible for publicly funded protection in one province may not be eligible in another. Seniors with similar health risks may face different access depending on their province. These differences are often dismissed as routine features of federalism. But as World Immunization Week approaches, RSV provides the opportunity to ask a broader question: who’s responsible for delivering equitable access to vaccines in Canada?Immunity and Society is a new series from The Conversation Canada that presents new vaccine discoveries and immune-based innovations that are changing how we understand and protect human health. Through a partnership with the Bridge Research Consortium, these articles — written by experts in Canada at the forefront of immunology, biomanufacturing, social science and humanities — explore the latest developments and their impacts.New tools, uneven accessRSV prevention now includes vaccines for older adults and pregnant people, and a monoclonal antibody (nirsevimab) that offers season-long protection for infants with a single dose.National guidance exists. The National Advisory Committee on Immunization recommends universal infant RSV immunization, but allows provinces to phase this in based on supply and cost. But these recommendations are advisory. Provinces ultimately decide what is publicly funded and for whom.The result is a patchwork. Some provinces have expanded infant coverage, while others have limited access to those considered high risk. Adult and maternal programs also vary in eligibility, delivery and funding.Cost plays a key role in these decisions. RSV therapies are expensive, and provinces must weigh them against competing health priorities. Epidemiological differences also matter, as do variations in disease burden and the additional challenges of vaccination in northern and remote communities. Not all variation is inherently problematic. But together, these factors mean that access to protection is shaped as much by provincial priorities as by medical need.When equity’s a goal but not a guaranteeIn immunization policy, equity generally means ensuring that those at higher risk, or facing barriers to access, are protected first, and financial or geographic differences don’t determine who receives care.RSV programs often emphasize protecting those at highest clinical risk, such as very young infants and people with underlying conditions. This approach is understandable. But it also narrows how equity operates in practice.In a system where provinces determine their own budgets and priorities, equity can become something negotiated rather than guaranteed. One province may fund broader access; another may limit eligibility based on cost-effectiveness or capacity. The same intervention is therefore available to some populations and not others.This shifts responsibility downward. Families must determine eligibility, navigate different rules, and sometimes absorb costs or logistical barriers to access. Equity becomes something people experience unevenly, rather than a guarantee built into the system.COVID-19 offers a cautionary example. Communities identified as highest risk were often vaccinated later than wealthier neighbourhoods during early rollout phases. This prompted provinces to introduce reactive “hotspot” strategies that in some cases replicated the same effect. Simply naming groups as “equity-deserving” did not ensure timely access. A pop-up vaccine clinic in a Toronto hotspot neighbourhood in April 2021. THE CANADIAN PRESS/Cole Burston Governance and accountabilityCanada’s immunization system involves multiple entities. Federal bodies approve products and issue recommendations. Provinces decide what to fund. Public health systems implement programs within local constraints.While each level plays an essential role, none is clearly responsible for national equity, creating a governance gap. Equity is widely endorsed, but no single body is accountable for delivering it nationally. RSV demonstrates how this plays out in practice — variation in immunization is accepted as a feature of federalism, rather than treated as a policy problem to be addressed.Procurement adds another layer. Vaccine pricing and contract terms are not routinely disclosed in Canada, and negotiations with manufacturers are often confidential. During COVID-19, federal vaccine contracts were released only after parliamentary pressure, with key details heavily redacted. Limited transparency makes it difficult to assess whether differences in access reflect pricing, negotiation leverage or policy choices. Read more: Consulting firms are the ‘shadow public service’ managing the response to COVID-19 Why it mattersRSV is one of the first major post-pandemic tests of Canada’s immunization system. It’s unlikely to be the last. New vaccines and antibody-based therapies are increasingly tailored to specific populations, making decisions about access more complex.As these technologies evolve, governance matters more, not less. Without clearer accountability, innovations risk reinforcing variation rather than reducing it. Read more: Flu, RSV and COVID-19: Advice from family doctors on how to get through this winter’s ‘tripledemic’ RSV highlights a broader challenge in Canadian immunization policy — equity is widely invoked, but responsibility for delivering it remains diffuse. Without clearer coordination, transparency and shared expectations, access to protection will continue to depend on where people live.For families of infants and seniors, that distinction is not abstract. It determines whether immunity is treated as a public good, or as a matter of postal code.Cora Constantinescu receives funding from bioMerieux, GSK, merck, Pfizer, Sanofi, with funds being transferred to her University organisation Sophie Webb does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.