Antiserum in the context of Immunosurgery

A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their shared reactivity between their surface antigens and a particular antiserum, allowing the classification of organisms to a level below the species. A group of serovars with common antigens is called a serogroup or sometimes serocomplex.

Serotyping often plays an essential role in determining species and subspecies. The Salmonella genus of bacteria, for example, has been determined to have over 2600 serotypes. Vibrio cholerae, the species of bacteria that causes cholera, has over 200 serotypes, based on cell antigens. Only two of them have been observed to produce the potent enterotoxin that results in cholera: O1 and O139.

Drug repositioning (also known as drug repurposing, re-profiling, re-tasking, or therapeutic switching) is the repurposing of an approved drug for the treatment of a different disease or medical condition than that for which it was originally developed. This is one line of scientific research which is being pursued to develop safe and effective COVID-19 treatments. Other research directions include the development of a COVID-19 vaccine and convalescent plasma transfusion.

Several existing antiviral medications, previously developed or used as treatments for severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), HIV/AIDS, and malaria, have been researched as potential COVID-19 treatments, with some moving into clinical trials.

In immunology, passive immunity is the transfer of active humoral immunity of ready-made antibodies. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and it can also be induced artificially, when high levels of antibodies specific to a pathogen or toxin (obtained from humans, horses, or other animals) are transferred to non-immune persons through blood products that contain antibodies, such as in immunoglobulin therapy or antiserum therapy. Passive immunization is used when there is a high risk of infection and insufficient time for the body to develop its own immune response, or to reduce the symptoms of ongoing or immunosuppressive diseases. Passive immunization can be provided when people cannot synthesize antibodies, and when they have been exposed to a disease that they do not have immunity against.

A blood product is any therapeutic substance prepared from blood, usually human blood; in some medicolegal contexts, the term refers specifically to human-blood-derived products. Blood products include whole blood, blood components, and blood plasma derivatives. Blood components include red blood cell concentrates or suspensions; platelets produced from whole blood or via apheresis; granulocytes; fresh frozen plasma; cryoprecipitates; antisera; and others. Some products for topical use, such as serum eye drops, have also been recently classified as blood components. Plasma derivatives are plasma proteins prepared under pharmaceutical manufacturing conditions, including: albumin; coagulation factor concentrates; and immunoglobulins.

Human blood and blood products come from blood donation, which can be from one person to another or from a person to themselves (such as when saving one's own blood for use after an upcoming surgical procedure).

Serum sickness in humans is a reaction to proteins in antiserum derived from a non-human animal source, occurring an average of 8 days after exposure. Symptoms often include a rash, joint pain, fever, and lymphadenopathy. It is a type of hypersensitivity, specifically immune complex hypersensitivity (type III). The term serum sickness–like reaction (SSLR) is occasionally used to refer to similar illnesses that arise from the introduction of certain non-protein substances, such as penicillin.

Serum sickness may be diagnosed based on the symptoms, and using a blood test and a urine test. It may be prevented by not using an antitoxin derived from animal serum, and through prophylactic antihistamines or corticosteroids. It usually resolves naturally, but may be treated with corticosteroids, antihistamines, analgesics, and (in severe cases) prednisone. It was first characterized in 1906.