Many people in winter get sick with influenza virus (the ‘flu’). The flu virus causes a lung infection with symptoms like fever, aches and a cough or sore throat. Most people get a mild infection and recover without treatment. But some people become very unwell and need to be in hospital. The sickest patients are admitted to an ICU for life-saving treatment. The World Health Organisation (WHO) estimates that each year as many as a billion people worldwide will catch influenza. Unfortunately, hundreds of thousands of people die every year from the flu.

Oseltamivir (sometimes sold under the name Tamiflu) is a medication that blocks the flu virus from multiplying in the body. It has been studied and widely used in lots of people with flu who are less unwell. In people with flu who do not need to be in hospital, oseltamivir was found to reduce the number of days they had symptoms (fever, cough, etc.) by less than 1 day. Because of this, it was hoped that oseltamivir may also improve outcomes in patients who are more unwell with flu and need to be admitted to hospital or ICU.

Some data, taken from observing the outcomes of patients who did and did not receive oseltamivir as part of their usual care, supported giving oseltamivir to patients with severe flu. As a result, a number of treatment guidelines recommend giving oseltamivir to patients who are critically unwell in ICU with flu. Before this trial (REMAP-CAP), there had never been a randomised clinical trial to test whether this treatment works in ICU patients with severe flu.

Adult patients at participating hospitals who were admitted to ICU with severe influenza and were eligible and willing to participate in the trial were randomly put into groups to either receive oseltamivir for 5 or 10 days (the usual care for many patients with severe influenza), or to not receive any oseltamivir. If a patient was too unwell to discuss participating, a family member, friend or other representative may have agreed to participating on their behalf. All other aspects of participants’ treatment followed usual care and were chosen by the doctors caring for them.

Data was collected about participants’ hospital stay from their medical records, and they were followed up to 90 days after being included in the trial.

This trial found that more ICU patients with severe influenza who received oseltamivir in the trial died within 90 days, compared to those patients who received usual care without oseltamivir. Based on this, it is highly likely that oseltamivir is harmful for these critically unwell patients.

The reason there were more deaths in the patients who received oseltamivir is not currently clear. We plan to conduct more research to understand the reason for this difference.

While we don’t yet know the reason for this difference, these results highlight why trials like REMAP-CAP are important. We need to test whether treatments are safe and work, including treatments that may already be widely used. We hope that these results will help to improve the care of patients who are critically unwell with flu in the future.

The results of this trial suggest that oseltamivir should not be given to adults with severe influenza who need to be admitted to an ICU.

It is important to note that these results do not provide any information about whether or not oseltamivir is helpful for patients with flu who are not critically ill. This includes patients with flu who are admitted to hospital but are not admitted to ICU, or those who have the flu but do not need to be admitted to hospital. There is already evidence supporting the safe use of oseltamivir in the community (outside of hospital) to prevent and treat flu.

Importantly, these results do not relate to children younger than 12 years old.

It is possible that oseltamivir has different effects for different patients. That may depend on their age, how unwell they are, whether or not their immune system is working properly, and how long they have been sick with flu.

REMAP-CAP continues to test whether or not oseltamivir is beneficial for other patient groups, including adults with flu who are admitted to hospital but are not in ICU, and children.

The REMAP-CAP trial results, that found oseltamivir does not work and may result in worse outcomes, relate only to patients aged 12 or older who are critically ill in an ICU.

It is likely that oseltamivir will continue to be prescribed for patients with the flu who are not critically ill in ICU. Oseltamivir has been well-studied in some other patient groups. For example, oseltamivir appears to work well when given to prevent flu infection after someone has been exposed to the influenza virus. Oseltamivir also shortens how long people with flu in the community (outside of hospital) have symptoms for.

If you, or someone you know, are currently taking oseltamivir for flu, and have any questions or concerns about this medication, please contact your healthcare provider.

Importantly, these results DO NOT relate to the flu vaccine. Vaccination remains the best way to avoid catching influenza and becoming sick with the flu.

The long-term effects of oseltamivir have not been studied, and in this trial we observed ICU patients for 90 days. The medication, oseltamivir, is broken down rapidly by the body, and so it is unlikely that the drug would have any effect after you stop taking it.

If you have any questions or concerns about any medications that you have received in the past, or are receiving now, please contact your healthcare provider.

The full results of this trial will be available on the REMAP-CAP website once they have been published in a medical journal. If you have any questions about these results, please email info@remapcap.org or contact the trial coordinators in your region. If you have any concerns about a medication that you are receiving, or have received, please contact your healthcare provider.

REMAP-CAP includes patients with respiratory tract infections who are admitted to participating hospitals.

If you are admitted to a participating hospital and are eligible to participate in REMAP-CAP, you may be approached to participate. However, it is currently not possible to volunteer to participate if you are not in hospital with a respiratory tract infection.

The REMAP-CAP investigators would like to acknowledge the important contribution of our participants, and research teams at participating hospitals for their help to generate important evidence to improve the care of future patients.