The method of transmission of antibodies from a recovered patient to an active patient has been used in the past to protect or treat dangerous pathogens of rabies, hepatitis B, measles, influenza, and many more. When COVID-19 was discovered and trials to find a cure began, convalescent plasma therapy was at the forefront. Now it is used in various countries to serve as the basis for an “immunity passport” or “risk-free certificate” from the novel coronavirus so that people can return to work and carry out daily activities. Many countries are still testing and reviewing the antibody response to SARS-CoV-2 infection in humans.
The patients who recover from COVId-19 illness develop some level of circulating neutralizing antibodies against protein cells of SARS-CoV-2. Following 2-3 weeks after the recovery, potential donors who are completely symptom-free and meet the standard blood donor eligibility, are listed and called for plasma collections. Even though the plasma therapy for COVID-19 is no silver bullet for the diseases, it shows improvements in many patients following the treatment with the plasma therapy.
Enough antibodies in the blood
To securely transmit the antibodies in patients, the plasma donor should have enough neutralizing antibodies in their blood. The US Food and Drug Administration (FDA) agency recommends neutralizing plasma donation antibody titers (measurement ratio) of at least 1:160. A 1:80 titer may be considered acceptable unless there is an alternative matched unit. It is still not clear whether a small amount of antibodies puts the recovered patients at risk of being infected. IF the neutralizing antibodies in the recovered patients aren’t of the desired level, the donors are asked to come again after two weeks.
The T-cell factor
T-cells act as soldiers in our body because they produce antibodies to protect against various infections and harmful viruses and pathogens. The T-cells have a kind of ‘memory’ which make them recognize and remember fighting off different viruses, so the second time they eliminate cells infected by the virus. An interesting new analysis of these memory T cells indicates that by recalling previous experiences with other human coronaviruses, they may protect certain people newly diagnosed with SARS-CoV-2. This may possibly explain why certain people tend to ward off the virus and could be less vulnerable to COVID-19 becoming seriously ill. Studies of SARS-CoV-1 immunity have shown that T cells hang on for several years longer than the antibodies they have produced. The studies showed that today, 17 years after the outbreak, those individuals still had lasting T memory cells. This memory T cells also recognized sections of SARS-CoV-2, acquired in response to SARS-CoV-1.
Even after all the positives of plasma therapy for COVID-19, scientists and researchers are trying to ensure full safety of the therapy, as known risks of plasma transfusion including allergic reactions, transfusion-associated circulatory overload (TACO), and transfusion-associated acute lung injury (TRALI) as with any plasma or blood transfusion, potential worsening of immune-mediated tissue damage via the poorly understood phenomenon of antibody-dependent enhancement (ADE), and blunting of endogenous immunity to the virus are of great concerns and yet to discovered and checked. The role of convalescent plasma treatment in these patients, however, is unclear, since all patients received at least one additional therapy, including antivirals, antibiotics or antifungals, and corticosteroids.
