The US National Institutes of Health (NIH) has increased the enrolment target in two clinical trials testing convalescent plasma as a treatment for hospitalised patients with Covid-19.

Preliminary observational data showed that convalescent plasma can help improve outcomes in severely ill and hospitalised Covid-19 patients.

However, additional randomised trials are needed to determine the effectiveness and safety of the treatment, noted NIH.

Convalescent plasma is the blood plasma of recovered people and contains antibodies that can neutralise the SARS-CoV-2 virus, which causes Covid-19, along with other potential immune response components.

The trials are backed by a fund of $48m under the US Government’s Operation Warp Speed (OWS) programme.

NIH director Francis Collins said: “The evidence on convalescent plasma as a treatment for severe cases of Covid-19 is promising but incomplete.

“We need to carry out rigorous randomised control clinical trials to determine how this therapy can improve outcomes.”

Participants enrolled at academic and community-based hospitals will be randomly given treatment or a placebo during the trials.

One trial, named Convalescent Plasma to Limit Covid-19 Complications in Hospitalised Patients, was initiated in April this year by NYU Langone Health in New York.

This trial will enrol about 1,000 Covid-19 patients with respiratory symptoms aged 18 or above. It will track clinical improvement at 14 and 28 days, apart from other outcomes, such as mortality and intensive care unit admission.

Another trial, called Passive Immunity Trial of Our Nation for Covid-19, will also recruit about 1,000 patients.

The trial will enrol participants aged 18 years or above who have been hospitalised or are likely to be admitted with acute respiratory infection symptoms and laboratory-confirmed Covid-19.

It will analyse clinical improvement at 15 days, along with ventilation/oxygen use, acute kidney injury, and cardiovascular events.

Results from the trials are expected by December.

In August, the NIH initiated a Phase III trial to evaluate various types of monoclonal antibodies for Covid-19 treatment.

Separately, a trial named AHEAD Study, funded by the NIH and Eisai, started dosing patients with BAN2401, a drug candidate that aims to delay or prevent the earliest memory loss in Alzheimer’s disease patients.