Plasma is the clear, straw coloured liquid portion of the blood that remains after the red blood cells, white blood cells, platelets and other cellular components are removed. It comprises 55 per cent of human blood and contains antibodies that can fight against diseases.

Covalescent plasma is the plasma drawn from the people who have recovered from a disease. It is rich in antibodies and has been used to treat or prevent serious infections and been part of medical practice for more than 100 years. Before vaccines, this was successfully used for infectious diseases like diphtheria, measles, polio and mumps.

In 1918, the Spanish Flu pandemic and even recently during the SARS and EBOLA outbreaks, it helped patients to recover. Now the idea is being revived by scientists as an effective treatment for patients hospitalised with COVID-19 or those who are at higher risk of getting the virus, like health care workers.

When a person is infected with COVID-19, the body creates blood proteins called antibodies to fight against the virus. It clears the virus and maintains antibody response, which approximately lasts for a year. The plasma is collected from patients who have recovered from COVID-19 and must be free of symptoms for at least 14 days. The red and white cells are separated and put back into the donor’s blood stream while the blood plasma, rich in antibodies, is stored for transfusion.

Survivors will be able to donate only twice, 400 ml each time, possibly saving 2-3 lives. The donor and the patient must be of compatible blood types, and the plasma is then tested for multiple diseases, including COVID-19, hepatitis and HIV. Next, it is again tested to make sure it has enough antibodies to effectively treat or prevent COVID-19. After that it is infused in the recipient. Vaccines also trigger the body to produce these antibodies. But currently there is no vaccine so it remains best source of antibodies for now.

Results are promising. A study published in the Journal of the American Medical Association on March 27 shows some evidence that plasma could help people with severe illness. Researchers in China report that five critically ill patients improved after receiving covalescent plasma. An online site has also been registered in the US where COVID-19 recovered people can register and donate their blood. Even the FDA has approved it for experimental trials. Besides China, Israel and the US have started to get positive results from the therapy. However, it’s not easy to find enough people who are eligible to donate. It is expensive and cannot be done on a large scale.

A number of drugs are now being tested in patients with COVID-19, but there is no robust evidence regarding its effectiveness. And even if a coronavirus vaccine is developed at lightning speed, it’s at least a year away. This covalescent plasma could be a vital treatment route until a better treatment, or vaccine, is available.