Recovered COVID-19 patients are donating their blood to help people who are struggling with the coronavirus. The red blood cells are removed and what’s left is a yellow liquid that may contain antibodies to SARS-CoV-2, the virus that causes COVID-19. This approach has been used in the past to treat Ebola, SARS and MERS so it is far from a new concept, but it’s currently the most accessible therapeutic option in hospitals.

Serum or plasma?

Serum (plural sera) is the liquid that is leftover from blood after it has clotted. Plasma is the liquid that is leftover but with clotting prevented by an anticoagulant. Plasma is usually collected by centrifuging the blood so that the cells separate from the liquid. Convalescent serum or plasma is the term for serum or plasma from someone who has recovered from a disease.

How it works

The important thing about plasma from recovered patients is that they may have antibodies specific to the SARS-CoV-2 virus that helped them recover. Antibodies are proteins that your immune system produces that can identify specific foreign particles like viruses or bacteria. Plasma could help prevent illness or help someone with high viral loads if the antibodies in the plasma attach to the viruses and essentially put them out of commission.

Think fast! Add Changing America to your Facebook and Twitter feeds to stay up-to-the-minute on the latest news and smartest insights.

A study in China of 10 nonrandomly selected people suggests that convalescent plasma therapy may help with recovery. Patients seemed to do better after three days, and the virus disappeared after seven days, but the authors warn that a randomized clinical trial is still needed to confirm its efficacy. Another study of five patients also showed promising results in critically ill patients whose body temperatures normalized within three days and viral loads decreased. This study also did not have a control group and was not randomized.

However, there’s not enough evidence yet to say that the current antibody tests available show immunity to the COVID-19 coronavirus.

The process for producing convalescent plasma

Currently, the Federal Drug Administration (FDA) is allowing the use of convalescent plasma from recovered COVID-19 patients as an investigational treatment for COVID-19. The eligibility requirements for who can donate blood is restricted to people who had laboratory confirmed cases and severe or life-threatening COVID-19. They must also give informed consent.

They also have to have recovered from all symptoms at least 28 days prior to donating, or 14 days prior with a laboratory confirmed negative result for a COVID-19 test. The ratio of antibodies in the plasma should be at least 1:160 in order for a detectable reaction, according to the FDA. This titer ratio means that if there’s one part antibodies, you can dilute it with 160 parts saline.

The blood from the recovered patient needs to get tested to check whether there are antibodies in their blood and in what quantities. There needs to be enough antibody in the plasma for it to be helpful as a treatment. After the plasma is tested, it gets stored and sent to hospitals where needed.

Timing matters for when you collect blood. “If you go from the beginning of the illness itself, you start seeing it between seven and 14 days with this virus,” says Jeffrey Henderson at Washington University School of Medicine to WIRED. “And then, we’re not sure how long the antibodies last. Sometimes they last a while at high levels. Sometimes they go up and come back down.”

BREAKING NEWS ABOUT CORONAVIRUS IN AMERICA

EXPERTS: 90 PERCENT OF US CORONAVIRUS DEATHS COULD HAVE BEEN AVOIDED

HERE'S WHEN THE CORONAVIRUS WILL PEAK IN YOUR STATE

PROTESTS AGAINST LOCKDOWN ORDERS GAIN SUPPORT FROM THE RIGHT

NOBEL LAUREATE PREDICTS MUCH FASTER US CORONAVIRUS RECOVERY THAN EXPECTED

HERE ARE THE BEST MAPS TO CHECK OUT THE CURRENT STATE OF THE CORONAVIRUS PANDEMIC

Treating COVID patients

There are a few ways that convalescent plasma can be used to treat people. One is preventive prophylaxis, in which it’s given to people who have been exposed to COVID-19 but haven’t developed disease yet. This approach is meant to try to prevent severe illness in the person receiving the plasma.

Doctors could also give convalescent plasma to patients in the emergency room to try to prevent their illness from progressing to the point of needing to be admitted to the intensive care unit. The other is using the plasma to treat people with very severe cases of COVID-19. If these patients have very high viral loads, meaning a lot of virus in their bodies, then the additional antibodies may help the body fight off the virus and lower the viral load.

Creating antibodies from scratch

There are companies exploring whether they can make antibodies to SARS-CoV-2 based on its genetic sequence. Another approach is to find the cells that are producing the right antibodies and clone those cells to produce more antibodies, according to virologist Kartik Chandran at Albert Einstein College of Medicine who spoke to WIRED.

Other things to consider

Receiving convalescent plasma therapy does not give a person immunity to the disease. To give someone immunity, the person’s immune system needs to be activated to respond to the pathogen. Giving plasma means giving antibodies, but it doesn’t confer immunity.

It’s like any other blood transfusion. It may help someone in the short term, but it’s dependent on supply and isn’t a long-term fix.

If you have recovered from COVID-19, you can find out where to donate plasma at this website by The American Association of Blood Banks.

For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.

You can follow Chia-Yi Hou on Twitter.

WHAT YOU NEED TO KNOW ABOUT CORONAVIRUS

FAUCI PREDICTS ANOTHER CORONAVIRUS OUTBREAK IN THE FALL WITH A 'VERY DIFFERENT' OUTCOME

HAVE I ALREADY HAD CORONAVIRUS? HOW CAN I TELL?

HERE ARE THE 6 WAYS THE CORONAVIRUS PANDEMIC COULD END

CAN YOU GET CORONAVIRUS TWICE?

CAN I SHOP FOR GROCERIES SAFELY DURING THE CORONAVIRUS PANDEMIC?

US MAY HAVE TO KEEP SOCIAL DISTANCING UNTIL 2022, NEW STUDY SAYS