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

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.

Inclusion criteria:

• Severe or critically ill COVID-19 patients tested positive in respiratory tract test.

• The COVID-19 patients who are not severe or critically ill, but in a state of immunity suppression;

• or have low CT values in the virus nucleic acid testing but with a rapid disease progression in the lungs.

• Severe or immediately life-threatening COVID-19, for example,

• Severe disease is defined as one or more of the following:

  • shortness of breath (dyspnea),
  • respiratory frequency ≥ 30/min,
  • blood oxygen saturation ≤ 93%,
  • partial pressure of arterial oxygen to fraction of inspired oxygen ratio < 300,
  • lung infiltrates > 50% within 24 to 48 hours

• Within 3 to 21 days from onset of symptoms

Exclusion criteria:

• Life-threatening disease is defined as one or more of the following: respiratory failure, septic shock, multiple organ dysfunction or failure

Critically ill COVID-19 patients will not considered suitable for being transfusion as inflammatory pathway is already set in, so antibodies will not make that much of difference.