Serological assays are tests that detect specific antibodies and are used to determine whether those antibodies are in an organism's blood; such tests require a significant concentration of unbound antibody in the blood serum. Serostatus is a term denoting the presence or absence of particular antibodies in an individual's blood. An individual's serostatus may be positive or negative. During<unk> , the specific antibody being tested for is generated. Therefore, before<unk> , the serological assay will not detect any antibody, and the individual's serostatus is seronegative for the antibody. After<unk> , sufficient concentration of the specific antibody exists in the blood, and the serological assay will detect the antibody. The individual is now seropositive for the antibody. During<unk> , when the amounts of antibody and antigen are very similar, it may not be possible to detect free antigen or free antibody. This may give a false negative result when testing for the infection. The time during which the amount of antibody and antigen are sufficiently similar that standard techniques will be unable to detect the antibody or antigen is referred to as the window period. Since different antibodies are produced independently of one another, a given infection may have several window periods. Each specific antibody has its own window period. Similarly, because standard techniques utilize assumptions about the specificity of antibodies and antigens and are based on chemical interactions, these tests are not completely accurate. Serological assays may give a false positive result, causing the individual to appear to have seroconverted when the individual has not. False positives can occur due to the test reacting to, or detecting, an antibody that happens to be sufficiently similar in structure to the target antibody. Antibodies are generated randomly, so the immune system has a low chance of generating an antibody capable of weakly binding to the assay by coincidence. More rarely, individuals who have recently had some vaccines or who have certain autoimmune conditions can temporarily test falsely seropositive. Due to the possibility of false positives, positive test results are usually reported as "reactive." This indicates that the assay reacted to antibodies, but this does not mean that the individual has the specific antibodies tested for. Seroreversion is the opposite of<unk> . During seroreversion, the amount of antibody in the serum decreases. This decrease may occur naturally as a result of the infection resolving and the immune system slowly tamping down its response, or as a result of loss of the immune system. Different infections and antigens lead to the production of antibodies for differing periods of time. Some infections may lead to antibodies that the immune system produces for years after the infection resolves. Others lead to antibodies that the immune system only produces for a few weeks following resolution. After seroreversion, tests can no longer detect antibodies in a patient's serum. The immune system generates antibodies to any antigen, so<unk>  can occur as a result of either natural infection or as a result of vaccination. Detectable<unk>  and the timeline of<unk>  are among of the parameters studied in evaluating the efficacy of vaccines. A vaccine does not need to have a 100%<unk>  rate to be effective. As long as a sufficient proportion of the population seroconverts, the entire population will be effectively protected by herd immunity. An individual being seropositive means that the individual has antibodies to that antigen, but it does not mean that that individual has immunity or even resistance to the infection. While antibodies form an important part of the immune system's ability to fight off and resolve an infection, antibodies and seropositivity alone do not guarantee that an individual will resolve the infection. An individual who is seropositive for anti-HIV antibodies will retain that infection chronically unless treated with medications specific to HIV. Conversely,<unk>  in other infections may indicate resistance or immunity. For example, higher concentrations of antibodies after<unk>  in individuals vaccinated against COVID-19 predicts reduced chance of breakthrough infection. Although<unk>  refers to the production of sufficient quantities of antibodies in the serum, the word<unk>  is often used more specifically in reference to blood testing for anti-HIV antibodies. In particular, "seroconverted" has been used to refer to the process of having "become HIV positive". This indicates that the individual has a detectable amount of anti-HIV antibodies. An individual may have a transmittable HIV infection before the individual becomes HIV positive due to the window period. In epidemiology,<unk>  is often used in reference to observing the evolution of a virus from a host or natural reservoir host to the human population. Epidemiologists compare archived human blood specimens taken from infected hosts before an epidemic and later specimens from infected hosts at later stages of the epidemic. In this context,<unk>  refers to the process of anti-viral antibodies becoming detectable in the human population serum.
Seroconversion
Reverse tolerance
Cross-tolerance
Sensitization 
Recrudescence
Peripheral tolerance
Antigenic escape
Cross-resistance