Doctors have treated the first UK patient in a reopened clinical trial that will explore whether blood plasma from “super donors” can help fight Covid in those with weakened immune systems.

Super donors produce exceptionally high levels of antibodies after infection and vaccination, and there are hopes that transfusions of their blood plasma can wipe out the virus in people whose own immune systems are compromised.

While two landmark trials known as Recovery and Remap-Cap found that convalescent plasma from people who recovered from Covid did not benefit other patients, a closer look at the Remap-Cap data showed that plasma with the highest levels of antibodies might help the immunosuppressed.

The findings prompted doctors to reopen the plasma arm of the Remap-Cap trial to investigate specifically whether donated plasma with extremely high levels of antibodies can save the lives of people with weakened immune systems and reduce the amount of time they spend in intensive care.

“It’s really important because this is a group of patients who are still dying from Covid,” said Prof Lise Estcourt, head of NHS Blood and Transplant’s clinical trials unit and chair of the new trial. “This is something that could be beneficial to them.”

The vulnerable group includes those with certain immune disorders and people who are on medicines that suppress immune defences, such as cancer and organ transplant patients. About half a million people in England are immunosuppressed.

More than 15 hospitals across the UK have agreed to take part in the trial, with more expected to join in the coming weeks. The first patient was transfused with plasma supplied by NHSBT at Charing Cross hospital in London.

The plasma used in the trial will come from patients who have been both infected with Covid and vaccinated against the virus, as this produces the highest concentrations of antibodies with the broadest effectiveness against different Covid variants. The donations will come from those who have already given blood, so there will be no fresh appeal for donors.

The highest level of antibodies seen so far in the reopened trial was in plasma donated by a man in his 20s. Tests found that his plasma contained more than 100,000 units of antibody per millilitre, about 100 times more than was seen in the first wave of the pandemic.

If the trial finds that the plasma works, it would be a valuable treatment, Estcourt said, because some immunosuppressed people do not respond to the vaccine and “monoclonal antibody” treatments, which are often given to patients, can be less effective against new variants.

“It could also be of particular use in the developing world, where access to more expensive treatments is limited,” she said.