AuthorisedTherapeutic use (Phase IV)Interventional

A Pragmatic Randomized Trial to Evaluate the Relative Effectiveness of Abrysvo® Revaccination Versus a Single Primary Dose for Preventing RSV-associated Lower Respiratory Tract Disease in Immunocompromised Adults (DAN-RSV IC REVAX)

Respiratory syncytial virus (RSV) is a common virus that usually causes mild, cold-like symptoms. However, for adults with weakened immune systems, RSV can be dangerous. It can spread deep into the lungs and cause severe chest infections that may require hospital care. A vaccine called Abrysvo is already approved to help protect against RSV. This clinical trial aims to discover whether giving an extra booster dose works better than a single dose for people whose immune systems are not working at full strength. Participants are adults aged 18 and over who are immunocompromised due to health conditions or medications. Researchers will follow participants across multiple winter virus seasons to see how well each vaccination approach prevents chest illnesses, GP visits, and hospital admissions. The findings will help doctors choose the best vaccine schedule to keep vulnerable people safe.

At a glance

Status

Authorised

Phase

Therapeutic use (Phase IV)

Sponsor

Region Hovedstaden, Pfizer Inc.

Enrolment target

29,000

Start

21 Sep 2026

Respiratory syncytial virus infection

What is this study about?

Respiratory syncytial virus, commonly known as RSV, is a widespread virus that affects the breathing passages. In most healthy people, it feels like a standard head cold with a runny nose, cough, and sore throat. However, for adults with weakened immune systems—such as those having chemotherapy, living with organ transplants, or taking medicines that suppress immunity—RSV can travel down into the lungs. This can cause severe illnesses like pneumonia or bronchitis, which often lead to emergency hospital care.

A vaccine called Abrysvo has been developed and approved to protect against RSV. While a single dose helps train the immune system to fight off the virus, people with reduced immunity may not get strong or lasting protection from just one jab. This study is testing whether giving a repeat vaccination (a booster dose) provides stronger, longer-lasting defence than one dose alone.

By comparing these two vaccination schedules, the study hopes to show how best to shield high-risk adults during the peak RSV season, which usually runs from autumn through spring. The results could help the NHS and health services worldwide decide on the most effective vaccination guidelines to prevent severe illness and reduce hospital pressures in winter.

Key takeaways

The study tests whether a booster dose of the Abrysvo RSV vaccine works better than a single dose.
It is aimed at adults aged 18 and over who have weakened immune systems.
Participants are monitored over multiple winter seasons for coughs, chest infections, and hospital visits.
The vaccine does not contain live virus and cannot cause RSV.
Joining is completely voluntary and will not change your standard NHS healthcare.

Who may be eligible?

This trial is designed for adults aged 18 and older who have a weakened immune system. You might be considered immunocompromised if you have certain long-term health conditions, or if you take medications such as immunosuppressants, steroids, or cancer therapies that lower your body's natural defences.

Both men and women can take part. To be eligible, you will need to be able to receive an injection and be willing to stay in touch with the study team to report any breathing or chest symptoms over the course of the study.

You may not be able to join if you have had a severe allergic reaction to vaccines in the past, or if you have specific medical conditions that the trial doctors feel would make participation unsafe. Your medical team or the trial team can look at your personal health history to confirm if this trial is right for you.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

You are aged 18 or older.
You have a weakened immune system due to an illness or medical treatment.
You are happy to receive an approved vaccine injection.
You are able to stay in touch with researchers over several winter seasons.
You can let the study team know if you develop chest or cold symptoms.

Answer every question to see your result.

What does participation involve?

Taking part in this study involves receiving the Abrysvo vaccine as an injection, usually into the upper arm. Because this is a randomised trial, participants are placed into different groups by chance: one group receives a standard single dose, while another group receives an additional revaccination dose.

After vaccination, you will be followed over two to three winter RSV seasons (typically between September and May). You will not need to spend long periods in clinic; instead, you will be asked to report any cold, flu, or chest symptoms if you feel unwell. The study team will track whether you need to see a GP or visit the hospital for lung infections. Follow-up usually involves short clinic visits, phone calls, or completing simple health diaries to monitor your wellbeing over a total period of up to three years.

Potential risks and benefits

Taking part may give you added protection against RSV lung infections, and the information gathered will help improve care for other vulnerable people in the future. However, there is no guarantee that an extra vaccine dose will offer greater protection. Like all vaccines, Abrysvo can cause temporary side effects, such as pain or redness at the injection site, tiredness, headache, or mild muscle aches. Serious allergic reactions are very rare. Taking part is entirely voluntary, and you are free to leave the trial at any time without your routine medical care or legal rights being affected.

Locations (1)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

—
Unverified
Denmark

Common questions

What is RSV?

RSV stands for respiratory syncytial virus. It is a common seasonal virus that causes coughs and colds, but can lead to severe lung infections in high-risk adults.

Can the Abrysvo vaccine give me RSV?

No. The vaccine does not contain any live virus, so it is impossible to catch an RSV infection from the jab.

Why is this trial focusing on people with weakened immunity?

People with lower immunity are at much higher risk of serious illness from RSV, and their bodies may need an extra booster dose to build adequate protection.

Will I know whether I am getting an extra booster dose?

The study team will explain the exact group you are in, as this is an open, practical study comparing different dosing schedules.

Will joining the study interfere with my normal treatments?

In most cases, you can carry on with your usual medications and NHS care as normal, but the trial doctor will review your full medical plan to be sure.