Updated May 2026 · ClinicalTrials.gov
COVID-19 Booster and IIV Schedule in Immunocompromised Hosts
The Immunogenicity and Safety of COVID-19 and Influenza Vaccine Co-administration and Interval in Immunocompromised Hosts
COVID-19 Booster and IIV Schedule in Immunocompromised Hosts (NCT06599658) is a Phase 2 interventional studying COVID 19 and Influenza, sponsored by McGill University Health Centre/Research Institute of the McGill University Health Centre. RECRUITING as of the most recent ClinicalTrials.gov update. Talk to your doctor before contacting the trial site.
About This Trial
The goal of this pragmatic embedded open-label, 2 x 2 factorial phase II randomized controlled trial is to evaluate strategies to improve COVID-19 booster and influenza vaccine immunogenicity in people living with immunocompromising conditions (PLIC). The main questions it aims to answer are: 1. Is co-administration of seasonal inactivated influenza vaccine (IIV) with the most up-to-date recommended COVID-19 booster dose non-inferior in inducing a 1-month peak protective humoral response against COVID-19, compared to a strategy of sequential administration of COVID-19 booster dose followed by seasonal IIV given one month later? 2. Is the administration of the most up-to-date recommended COVID-19 booster doses at 3-month intervals superior at maintaining a longer term protective humoral immune response, compared to booster doses administered at 6-month intervals? Researchers will compare (1) COVID-19 and Influenza vaccines administered at Day 0 + COVID-19 Booster at a 3-month interval, (2) COVID-19 vaccine administered at Day 0 and Influenza vaccine administered at Day 28 + COVID-19 Booster at a 3-month interval, (3) COVID-19 and Influenza vaccines administered at Day 0 + COVID-19 Booster at a 6-month interval, and (4) COVID-19 vaccine administered at Day 0 and Influenza vaccine administered at Day 28 + COVID-19 Booster at a 6-month interval to see if median neutralization capacity of patient sera is non-inferior in the co- vs. sequential administration arms at 1-month after the initial COVID-19 booster and superior in the 3-month interval arms vs. the 6-month interval arms at 12 months after the initial COVID-19 booster. These outcomes will also be compared at 2-months for question 1 and 6-months for question 2. People living with immunocompromising conditions who take part in the trial will have blood samples drawn to verify immune response, be monitored for changes in clinical events and therapies, and complete questionnaires to verify adverse effects, quality of life and economic impact.
What Stage of Research Is This?
Phase 2 trials evaluate whether a treatment actually works against COVID 19 and continue monitoring side effects. Phase 2 enrolls larger groups (typically 100–300 patients) and produces the first real efficacy signal. A successful Phase 2 readout is what unlocks the much larger Phase 3 confirmatory trials needed for FDA approval.
This trial is currently recruiting participants. The sponsor has registered the study with ClinicalTrials.gov as actively enrolling, which means new applicants who meet the eligibility criteria can be considered for screening. Trial status can change between updates — confirm current recruiting status with the study contact before traveling for a screening visit.
A target enrollment of 660 participants makes this a sizable late-stage trial. Studies in this range typically have enough power to detect clinically meaningful differences from a comparator and to characterize less-common side effects.
Who May Be Eligible (Plain English)
These are translations of the protocol\'s inclusion and exclusion criteria, simplified for patients and caregivers. The original clinical text appears below. Eligibility is ultimately confirmed by the trial site\'s screening process — this summary is a starting point for a conversation with your doctor, not a final determination.
Original Eligibility Criteria
View original clinical language
Treatments Being Tested
Inactivated influenza vaccine (IIV) at baseline
National Advisory Committee on Immunization (NACI) recommended seasonal inactivated influenza vaccine for moderate to severely immunocompromised patients by age at baseline
COVID-19 Vaccines at a 3-month interval
Updated NACI recommended COVID-19 booster for moderate to severely immunocompromised patients at a 3-month interval
Inactivated influenza vaccine at Month 1
National Advisory Committee on Immunization (NACI) recommended seasonal inactivated influenza vaccine for moderate to severely immunocompromised patients by age 1-month following initial COVID-19 booster
COVID-19 Vaccines at a 6-month interval
Updated NACI recommended COVID-19 booster for moderate to severely immunocompromised patients at a 6-month interval
Locations (3)
Trial sites listed on ClinicalTrials.gov for this study. Site activation status can vary — confirm with the specific site before traveling for a screening visit.
How to Talk to Your Doctor About This Trial
Bring the printable summary of this trial — including the NCT ID (NCT06599658), the sponsor (McGill University Health Centre/Research Institute of the McGill University Health Centre), and the key eligibility criteria — to your next appointment. Your doctor can review the inclusion and exclusion criteria against your medical history, lab values, and current treatments to assess whether you are likely to qualify. They can also help you weigh whether trial participation makes sense alongside your existing care plan.
Useful questions to walk through together: What does the trial protocol require beyond standard care? How long is the active treatment phase, and how long is follow-up? Are there study visits at sites I can reach? Who pays for the trial-specific procedures, and who pays for standard-of-care portions? See our 25 questions to ask about clinical trials guide for a more complete checklist.
Authoritative Sources
The official record for this trial lives on ClinicalTrials.gov — the federal registry maintained by the National Library of Medicine at NIH. For background on how this trial fits into the FDA approval pathway, see the FDA drug approval process. For oncology-specific guidance for patients considering trials, the National Cancer Institute publishes patient-oriented overviews. International trial registries are aggregated by the WHO ICTRP.
Frequently Asked Questions
What is the NCT06599658 clinical trial studying?
The goal of this pragmatic embedded open-label, 2 x 2 factorial phase II randomized controlled trial is to evaluate strategies to improve COVID-19 booster and influenza vaccine immunogenicity in people living with immunocompromising conditions (PLIC). The main questions it aims to answer are: 1. Is co-administration of seasonal inactivated influenza vaccine (IIV) with the most up-to-date recommended COVID-19 booster dose non-inferior in inducing a 1-month peak protective humoral response against COVID-19, compared to a strategy of sequential administration of COVID-19 booster dose followed b… The full protocol is registered on ClinicalTrials.gov and includes the primary outcome measures, eligibility criteria, and study endpoints.
Who can participate in NCT06599658?
Eligibility for this trial depends on the specific inclusion and exclusion criteria set by the sponsor. The plain-English summary above translates the most important criteria into accessible language; the official clinical text is preserved in the collapsible section underneath. Whether you fit any specific trial is a medical decision your doctor needs to confirm — bring the trial information to your treating physician for a full review against your medical history.
How do I contact the trial site for NCT06599658?
Contact information registered with ClinicalTrials.gov is shown in the sidebar of this page. Before reaching out, confirm with your treating physician that this trial is appropriate for your situation. The trial site will then walk you through the screening process to determine final eligibility.
Is participating in a clinical trial safe?
Clinical trials in the United States are regulated by the FDA and overseen by Institutional Review Boards (IRBs) that review the protocol for safety. Risk varies by trial — Phase 1 studies test new treatments in humans for the first time, while Phase 3 trials use treatments that have already passed earlier safety screening. The informed consent document for any specific trial details the known risks and what to expect. Discuss those risks with your physician before deciding whether to participate.
Where can I verify the data on this page?
Every detail on this page comes directly from the ClinicalTrials.gov API. Click "View on ClinicalTrials.gov" in the sidebar to see the official, unmodified record. The federal record is always authoritative; this page is a structured presentation with a plain-English eligibility translation. For background on how clinical trials are regulated, see the FDA drug approval process documentation.
How This Page Is Built
Every field on this page is pulled directly from the ClinicalTrials.gov API v2 — no estimates, no proxies. The plain-English eligibility translation is generated from the original protocol text and reviewed for fidelity to the underlying clinical criteria. The original clinical text remains visible in the collapsible section above so users and clinicians can verify the translation. Read the full methodology for the data pipeline and known limitations.
Source: ClinicalTrials.gov API v2 record for NCT06599658. Maintained by the National Library of Medicine at NIH. Public domain. Cite as: "TrialFinderData. NCT06599658. Data: ClinicalTrials.gov."
Medical disclaimer: This page is informational, not medical advice. Talk to your doctor about whether a clinical trial is right for you.
Last updated 2026-05-08 · Data from ClinicalTrials.gov.