Convalescent Plasma for Passive Immunization in COVID-19 ICU Patients: An Interventional Study

Passive immunization involves the administration of antibodies against a given agent to a susceptible individual for the purpose of preventing or treating an infectious disease due to that agent. A general principle of passive antibody therapy is that it is more effective when used for prophylaxis than for treatment of disease. When used for therapy, antibody is most effective when administered shortly after the onset of symptoms. The reason for temporal variation in efficacy is not well understood but could reflect that passive antibody works by neutralizing the initial inoculums, which is likely to be much smaller than that of established disease . As an example, passive antibody therapy for pneumococcal pneumonia was most effective when administered shortly after the onset of symptoms, and there was no benefit if antibody administration was delayed past the third day of disease.

Therapeutic and prophylactic significance was explored in influenza and measles . Transfusion of immune plasma is a standard treatment modality for various viral hemorrhagic fevers . Its efficacy in treating Ebola Virus Disease is also well established . Studies have reported reduction viral load in patients with H1N1 influenza .Efficacy of convalescent plasma has been anecdotally reported in SARS-CoV-2 infections .

The largest study involved the treatment of 80 patients with SARS in Hong Kong. Patients treated before day 14 had improved prognosis defined by discharge from hospital before day 22, consistent with the notion that earlier administration is more likely to be effective .

In the case of SARS-CoV-2, the anticipated mechanism of action by which passive antibody therapy mediated protection is viral neutralization. However, other mechanisms may be possible, such as antibody-dependent cellular cytotoxicity and/or phagocytosis. The only antibody type that is currently available for immediate use SARS-CoV-2 is that found in human convalescent sera.

In China for SARS-CoV-2 disease, it has been found that the convalescent plasma therapy is effective for patients with a disease course exceeding three weeks and whose virus nucleic acid tests continuously to show positive from respiratory tracts specimen. It can speed up virus clearance, increase the numbers of the plasma lymphocytes and NK cells, reduce the level of plasma lactic acid, and improve renal functions.