**3. Historical perspectives of CP**

Serum therapy was the only effective treatment option for infectious diseases prior to the discovery of antibiotics. In the year 1890, serum therapy was founded by Emil von Behring. The use of serum blood therapy has been proposed for treating diphtheria. At the same time Behring and Kitasato developed an effective therapeutic serum against tetanus.

Documented reports of the Spanish flu H1N1 pandemic (1918–1920) stated that transfusion of influenza-convalescent human blood products (whole blood, plasma, or serum) reduced morbidity and mortality. Hence, convalescent plasma could be an effective therapy during viral outbreaks and pandemics [17]. Treatment of severe H1N1 infection with convalescent plasma revealed that 1 dose of convalescent plasma with >1:160 neutralizing antibody was successful in reducing mortality and the viral load of the respiratory tract decreased by >3log10 copies/mL within 48 h of plasma therapy [18]. H5N1-infected BALB/c mice treated with H5N1-specific F(ab')2 fragments derived from horses provided proof that passive immunotherapy is effective for immunologically competent and incompetent hosts [19].

A Lyophile serum was used effectively to prevent and/or treat many diseases such as measles, chickenpox, mumps, German measles, erysipelas, hemolytic streptococcal infections and scarlet fever [20]. Argentine hemorrhagic fever (AFH) caused by Junin virus is one of the few infectious viral disease in which CP administration is a specific treatment of choice that can neutralize viremia after immune plasma transfusion [21]. CP has been used with varied outcomes in combating Lassa fever and Ebola virus [22, 23]. For most viral diseases, the first week of infection peaks with viremia. The patient typically produces a primary immune response by day 10–14 followed by virus clearance.

In the SARS-CoV-1 outbreak, CP therapy was used and found to be more effective in patients who received transfusions within 14 days of the onset of symptoms [24]. The analysis further revealed that virus was cleared 1 day after CP transfusion, preceded by fever subsidence and pulmonary infiltrate resolution. CP transfusion may be considered as alternative treatment in cases where SARS-CoV patients experience severe deterioration and fail to respond to the available treatment such as ribavirin or methylprednisone [25].

*Convalescent Plasma Immunotherapy - A Possible Mitigation Strategy for SARS-CoV-2 Pandemic DOI: http://dx.doi.org/10.5772/intechopen.98254*

Meta-analysis by Nottingham University-World Health Organization Collaborating Center showed that CP containing MERS-CoV-specific antibodies from recovered patients could be the most promising near-term therapy for infected individuals. In MERS-CoV patients, treatment with CP was restricted by a limited pool of donors with adequate antibody levels [26] and the usage of CP in three critically ill respiratory failure MERS-CoV patients in South Korea resulted in significant clinical improvements [27].
