Systematic Review Set to Map Vaccine Adherence Across Cancer Treatment Phases
Adults receiving cancer care often move through two very different immunologic states: active treatment, when cytotoxic therapy, targeted agents, steroids, or marrow suppression can blunt host defenses, and follow-up, when recovery may be incomplete and preventive care can still lag. This BMJ Open protocol sets out to examine how well vaccination schedules are followed across both phases, with a focus on adult oncology populations and a broad range of vaccines, including age-based and seasonal immunizations.
The clinical problem is straightforward. Patients with cancer face a higher burden of infection risk, yet recommended vaccines are frequently missed, delayed, or left incomplete. Immunization is not a decorative extra in this setting; it is one of the few interventions that can reduce avoidable respiratory and vaccine-preventable disease in people whose immune response is already compromised by malignancy or its treatment. A review that isolates adherence rather than simply vaccine eligibility is especially useful because real-world protection depends on whether schedules are actually completed on time.
Why Adherence Is Harder in Oncology Than in General Practice
Cancer care fragments time, responsibility, and follow-up. Vaccination decisions may be shared between oncologists, primary care clinicians, infusion teams, and community physicians, and the result is often missed opportunity rather than deliberate refusal. Treatment schedules can also disrupt routine preventive care: appointments cluster around chemotherapy cycles, acute toxicities dominate attention, and vaccines may be deferred because of concern about timing, response, or safety.
In that context, adherence becomes a moving target. A patient may be partially vaccinated before a diagnosis, defer doses during active therapy, and never fully re-enter a preventive care pathway once treatment ends. The protocol’s decision to examine both active oncologic treatment and post-treatment follow-up is clinically important because those periods are not interchangeable. Immune function, clinic access, and care priorities differ sharply between them, and vaccine uptake may fall for different reasons in each phase.
The planned review will cover multiple vaccine types, including seasonal and age-based vaccines, rather than narrowing the analysis to a single product. That broader lens should better reflect the immunization needs of adults living with cancer, where influenza, pneumococcal, and other routine vaccines may all matter in the same patient. It also increases the chance of identifying structural barriers that cut across vaccine categories, such as counseling gaps, scheduling failures, or inconsistent documentation.
Search Strategy Designed to Capture a Broad Adult Oncology Evidence Base
The protocol calls for a comprehensive search across major international and regional databases, without language or date restrictions. That approach is likely to reduce the risk of missing studies from different health systems, where vaccination practices and oncology workflows may differ substantially. It also creates room to identify older data that still inform current care, especially in areas where vaccine delivery in cancer populations has changed slowly.
Independent study selection, data extraction, and risk-of-bias assessment are built into the design. Those steps matter because adherence studies often vary in how they define “up to date,” “complete,” or “recommended,” and extraction errors can distort pooled estimates quickly when definitions are inconsistent. A dual-review process should help guard against avoidable classification mistakes and should make the final synthesis more defensible.
The protocol also anticipates a familiar obstacle in evidence synthesis: heterogeneity. Cancer type, treatment intensity, vaccine schedule, outcome definitions, and follow-up length may all vary widely from one study to the next. A transplant recipient receiving an intensive regimen is not comparable to a patient in long-term survivorship, and a seasonal influenza series does not map neatly onto a multi-dose age-based schedule. Quantitative pooling may therefore be limited in some segments, with narrative synthesis likely needed where the data cannot be meaningfully combined.
Immune Suppression, Care Transitions, and Missed Prevention Opportunities
In oncology, vaccine adherence is not simply a behavioral metric. It sits at the intersection of immune suppression, clinic logistics, patient education, and clinical caution. During active treatment, vaccine timing can be constrained by concerns about immunogenicity or hematologic toxicity, while during follow-up the problem often shifts toward inertia and care handoff. The biology is unforgiving: a delayed vaccine can mean a missed window of protection during a period of heightened susceptibility.
The protocol’s focus on adult patients is also sensible. Adult vaccination schedules are already more complex than pediatric schedules, and cancer care adds another layer of complexity. Many adults have incomplete histories before cancer is diagnosed, and once treatment starts, the vaccination record may be dispersed across different clinicians and settings. A systematic review in this population can help clarify whether the problem is persistent underuse, phase-specific drop-off, or both.
One sentence captures the practical stakes. Missed vaccination in cancer care can translate into preventable infection during a period of biologic vulnerability.
What This Review Could Clarify for Oncology Teams
If the planned synthesis succeeds, it may provide a clearer picture of where vaccine uptake breaks down most often: at treatment initiation, during prolonged therapy, or after the active phase has ended. It may also identify whether adherence differs by vaccine type, which would be clinically important for clinics trying to design standing orders or survivorship protocols. Even without a meta-analytic summary in every subgroup, a structured review can still expose patterns that are invisible in single-center audits.
For oncology teams, the most useful output may be less about a single pooled percentage and more about a map of failure points. Are vaccines offered but declined? Recommended but not documented? Deferred during therapy and never resumed? Each pathway implies a different intervention, from better medication reconciliation and survivorship planning to standardized vaccination counseling integrated into oncology visits.
A second sentence speaks for the bedside reality. If vaccination is not built into cancer care workflows, it tends to disappear between appointments.
The protocol does not yet provide results, so clinical impact remains prospective. Its value lies in the methodical attempt to assemble a dispersed literature into a usable synthesis, while acknowledging in advance that wide variation in cancer diagnosis, treatment regimen, vaccine type, and adherence definition may limit how much can be pooled statistically. For clinicians, that limitation is not a flaw so much as a realistic preview of the evidence base they already work within.
Data Gaps That Will Shape Interpretation
Any review in this field will still face the same unresolved questions: which vaccines are most consistently missed, whether adherence improves after treatment ends, and how often incomplete vaccination reflects patient refusal versus system failure. Language and date-unrestricted searching may broaden coverage, but it will not erase the underlying variability in study design. The final synthesis will need to separate true adherence failure from differences in how studies measured it.
That methodological challenge is especially relevant in oncology, where vaccination guidance can change over time and practice patterns may lag behind updated recommendations. The review’s strength lies in its breadth; its interpretive caution will need to be just as broad. For now, it sets up a needed evidence map for vaccination adherence in adults under active oncological treatment and follow-up, a population where preventive care is often as clinically important as the anticancer regimen itself.