Swine flu deaths can be prevented by giving severely ill victims blood plasma from recovered patients, new research has shown.
The transfusion "vaccine" containing antibodies against the virus more than halved death rates among hospital intensive care patients.
Although the study was small, the Chinese authors say "convalescent plasma" treatment could help to save patients with potentially fatal flu infections.
Since the start of the flu season last October, 112 people have died with the virus in the UK. Of these, 95 had the pandemic H1N1 swine flu strain.
Swine flu, which emerged in April 2009, has been linked to more than 13,000 deaths around the world, according to Health Protection Agency figures released in January 2010.
During the 2009/2010 season a total of 360 people in the UK lost their lives after catching the virus.
Most of those infected by swine flu suffer mild symptoms and quickly recover. But in some cases the virus can lead to life-threatening conditions such as pneumonia or kidney failure.
Convalescent plasma therapy involves giving severely infected patients transfusions of plasma from others who have recovered from the same infection.
Plasma is the yellowish liquid component of blood, stripped of the blood cells that are normally suspended in it.
The aim of convalescent plasma therapy is to transfer protective antibodies from one individual to another.
Antibodies are immune system proteins that neutralise harmful foreign bodies such as viruses or mark them out for destruction.
The new study involved 93 seriously ill swine flu patients who needed intensive care in Hong Kong hospitals between September 2009 and June 2010.
Of these, 20 agreed to receive 500 millilitre transfusions of plasma donated by patients who had earlier fought off the H1N1 virus. The remaining 73 who declined treatment acted as comparison "controls".
In total, 20% of the treated group died - less than half the proportion of control patients, 55% of whom lost their lives.
Viral load, a measurement of the number of active viruses in the blood, also decreased at a faster rate among patients given the plasma transfusions.
None of the treated patients developed any adverse reactions.
The researchers, whose findings are reported in the journal Clinical Infectious Diseases, wrote: "This study has demonstrated that convalescent plasma treatment may have a place in the treatment of patients with severe H1N1 2009 infection."
The treatment both reduced viral load and dampened dangerous inflammatory responses, said the scientists.
Natural antibodies were also less likely than those in artificial vaccines to allow the survival of an "escape mutant" strain of the virus.
Study author Dr Kowk-Yung Yuen, from the University of Hong Kong, said: "One of the benefits of convalescent plasma treatment in patients with severe influenza A infection is that it does not suffer from the problem of drug resistance.
"Additionally, it would remain effective until the virus has changed significantly enough to affect immunity. This form of treatment may be useful in future novel viral infections."