SINGAPORE - Blood plasma from recovered Covid-19 patients is reserved for those who are not responding well to initial treatments for the coronavirus, the National Centre for Infectious Diseases (NCID) has said.

In convalescent plasma therapy, the blood plasma, which may contain antibodies against Covid-19, is given to infected patients to help them recover faster.

It is used to complement initial treatments of steroids and antivirals, and administered as part of a monitored programme from the NCID and Tan Tock Seng Hospital, in collaboration with the Health Sciences Authority and Duke-NUS, said Dr Shawn Vasoo, clinical director of NCID, in response to queries from The Straits Times last week.

Seven patients have been treated under the programme so far, though it is unclear how effective the treatment has been for them.

Steroids such as dexamethasone, and antivirals like remdesivir, have typically been used on Covid-19 patients requiring oxygen support.

Professor Wang Linfa, from the Programme of Emerging Infectious Diseases at the Duke-NUS Medical School, said the blood collected from recovered patients is measured for neutralising antibodies, which are able to block the Sars-CoV-2 virus from binding to a cell surface receptor known as ACE2.

For the treatment to be effective, the level of antibodies must show at least a 1:80 titre reading, a measure of the dilution of the antibodies in the blood plasma.

So far, 27 recovered patients have donated their blood, and the blood can be stored for up to one year. Some of the donors donated several times, said Dr Vasoo.

He noted that many patients who had mild infections may not have enough of the neutralising antibodies in their blood, making it challenging to find suitable donors.

And as a blood product, the convalescent plasma will carry "certain other risks" such as transfusion reactions, though there have been no such cases among the patients treated in Singapore so far, said Dr Vasoo.

He noted that transfusion reactions have generally been uncommon. They have occurred more frequently in children rather than adults, according to studies conducted among large cohorts.

A clinical trial in Argentina found that blood plasma with high titres of antibodies, when administered to older infected patients within 72 hours of the onset of symptoms, was able to reduce their risk of progression to severe respiratory disease.

The study's findings were published in the New England Journal Of Medicine on Jan 6.

But a clinical trial found that those already severely ill with Covid-19 did not benefit from the blood plasma.

The international trial involving 900 patients in intensive care found that those treated with blood plasma did not show improved outcomes, Reuters reported on Jan 11.

Initial analysis found a low probability of 2.2 per cent that the blood plasma was able to reduce death rates or the number of days patients needed intensive care.

The blood plasma's effect in patients with less severe symptoms continues to be explored in the ongoing trial.