a fourth-generation test after the window period. similarly, individuals taking pre-exposure prophylaxis (prep) can experience extended window periods compared to the average population, leading to ambiguous testing. thus, individuals who test negative for hiv before the window period ends for that specific test will usually need to be retested after the window period, as they may fall into the minority who take more time to develop antibodies. current cdc recommendations are to begin with a test that screens for both antigen and antibody, then follow up with an immunoassay to differentiate between hiv-1 and hiv-2 antibodies. non-reactive (negative) tests are followed up with nucleic acid tests for viral rna. about 70-80% of people infected with hiv will experience symptoms during the seroconversion period within about two to four weeks, primarily associated with a high viral load and the immune system's acute response to the infection. these symptoms can last for anywhere from a couple of days to several weeks. some people have no symptoms at all. the symptoms of seroconversion are non-specific and can often be mistaken for a more benign illness such as the flu. symptoms can include lymphadenopathy (swelling of the lymph glands), general fatigue and malaise, chills, low-grade fever, sore throat, body aches, night sweats, ulcers in the mouth, pain in the joints and muscles, loss of appetite, headache, and a maculopapular rash on the trunk of the body. because not all individuals experience the symptoms of seroconversion, and because they are non-specific, individuals should receive testing for hiv if they are high-risk or have possibly had an exposure to hiv. likewise, if an individual suspects exposure for hiv, a lack of symptoms does not indicate that seroconversion has not occurred. 20-30% of people undergoing hiv seroconversion lack symptoms entirely or have mild symptoms. the immune system mounts an acute effort to resolve the hiv infection during the seroconversion period. following this period, the immune system temporarily contains the infection. the symptoms of seroconversion lessen and disappear in most people, with hiv entering a stage of clinical latency. at this stage, the infection remains within the body without causing symptoms, and the viral load gradually increases. the body continues producing anti-hiv antibodies throughout clinical latency, and the hiv infection remains detectable. individuals who have become hiv seropositive may benefit from seroconversion testing for comorbid infections for which they are suspectible. for example, positive seroconversion of human herpesvirus 8 is highly predictive of later development of kaposi's sarcoma, allowing for individuals who are seropositive to be aware of their risk of developing kaposi's sarcoma and thus receive appropriate monitoring. seroconversion in covid-19 as with other viruses, seroconversion in covid-19 refers to the development of antibodies in the blood serum against covid-19 antigens. an individual is seropositive, or has seroconverted for covid-19, once standard techniques are able to detect covid-19 antibodies in the blood. seroconversion testing is primarily used to detect individuals who have been infected with covid-19 in the past who have already resolved their infections. due to the time delay of seroconversion compared to viral load, seroconversion is not sufficiently timely to diagnose a current case of covid-19. however, seroconversion may be helpful for individuals with suspected infections who are negative by rt-pcr testing for viral load. not all people who are infected with sars-cov-2 become seropositive. conversely, some individuals can become seropositive without ever experiencing symptoms of covid-19 or knowing that they were exposed to covid-19 at any point. some asymptomatic individuals can still transmit covid-19 to others. however, it is unclear whether all asymptomatic individuals who seroconvert to covid-19 had transmissibility at any point (active infection), or whether an individual can seroconvert to covid-19 without undergoing a period during which they can infect others. most standard assays for covid-19 seroconversion test for antibodies against the covid-19 specific spike protein (s) and the covid-19 specific nucleoprotein (n). concentrations of antibodies develop after several days and reach their maximal value approximately two to three weeks after infection. some individuals have detectable levels of both igg and igm as early as within the first week after symptoms begin. although viral infections typically have a rise in igm that precedes a rise in igg, some individuals infected with covid-19 have both igm and igg responses at approximately the same time. after initial seroconversion for either igm or both igg and igm, concentrations continue to rise and peak within one week after antibodies first become detectable. concentration of igm tend to fall within three weeks after symptoms first begin regardless of resolution to the covid-19 infection. levels of igg plateau and remain high for at least six to seven months after the resolution of the infection in most individuals. the length of time that anti-spike igg remains high varies greatly between different individuals. older individuals and individuals with less robust immune systems tend to serorevert within a shorter period of time. becoming seropositive for covid-19 antibodies can occur due to either infection with covid-19 itself or due to becoming vaccinated to covid-19. being seropositive for covid-19 does not intrinsically confer immunity or even resistance. however, higher rates of seroconversion are linked to greater clinical efficacy of vaccines. this suggests that for most individuals, seroconversion does lead to resistance. studies of the available covid-19 vaccines have indicated that vaccination causes a stronger seroconversion with a heightened peak concentration of igg antibodies, as well as a longer plateau of resistance compared to seroconversion from a natural infection of covid-19. the timeline of seroconversion is similar between seroconversion from infection and seroconversion from vaccines. antibodies first becoming detectable within approximately two to three weeks. younger individuals tend to have more robust responses to vaccinations compared to older individuals. the difference in the robustness of the response increases with the second dose. younger individuals tend to have much higher and more sustained peaks of anti-spike igg antibodies following the second dose. many otherwise ill individuals, such as those with cancer or chronic liver disease, still exhibit similar rates of seroconversion to the general population. on the other hand, individuals with weakened immune systems, such as due to immunosuppressive medications or leukemia, can exhibit decreased rates of seroconversion for currently available vaccines. the different vaccines currently utilized do not appear to have significant differences in seroconversion rates when compared in similar population groups. seroconversion does not necessarily occur at the same rate to all covid-19 antigens. individuals who seroconvert more rapidly to different antigens may have different disease courses. individuals infected with covid-19 who developed primarily anti-spike antibodies rather than anti-nucleocapsid antibodies are less likely to have a severe disease course. studies suggest that anti-spike antibodies confer greater resistance to covid-19 than anti-nucleocapsid antibodies. a higher ratio of anti-spike antibodies to anti-nucleocapsid antibodies thus serves as a predictor of disease course and patient mortality. as a result, currently available vaccines target the production of anti-spike antibodies rather than anti-nucleocapsid antibodies. not all individuals who are infected to covid-19 seroconvert, including individuals who otherwise fully recover from covid-19. this could suggest that the individuals are developing antibodies that standard techniques do not cover, that individuals can recover with extremely low levels of antibodies not detectable by standard techniques, or that individuals do not need antibodies against covid-19 in order to recover. individuals who recover from covid-19 but never seroconvert tend to have lower viral loads and be of younger age than individuals who do seroconvert. this may indicate that individuals who have experienced less severe covid-19 infections are less likely to trigger full responses from their immune systems and that these individuals manage to clear the infection despite not producing sufficient quantities of antibodies or any specific antibodies against covid-19 at all. significantly older patients of greater than eighty years old are more likely to have higher quantities of igg antibodies compared to younger patients at the time of infection. this is consistent with the fact that older patients tend to have more severe covid-19 infections and thus have higher viral loads compared to younger patients. however, this increased antibody load tends to decrease after about three months post-recovery compared to younger patients, compared to the six to seven months observed in the general population. this implies that the resistance may not last long-term in older individuals, leaving them suspectible to subsequent covid-19 infections. some studies have disputed the link between concentrations of antibodies of either igm or igg and the severity of the disease course. several studies have demonstrated that individuals who recovered from covid-19 infections and are seropositive for covid-19 at the time of vaccination produce significantly more anti-spike igg antibodies in response to vaccination than individuals who are not seropositive for covid-19, while individuals who have recovered from covid-19 infections but never seroconverted and are seronegative respond similarly to individuals who have never been exposed to covid-19. specifically, individuals who are seropositive for covid-19 at the time of their first dose of vaccination have a response similar to the general population's response to the second dose, due to this increased concentration of igg antibodies. some individuals who have recovered from covid-19 may decline vaccination due to the belief that their recovery from infection has a protective effect. nevertheless, the lack of seroconversion for all former infectees indicates that recovery from infection alone does not guarantee resistance to covid-19. even for individuals who seroconverted, seropositivity is at best only as protective as a single dose of vaccine, as opposed to the more robust protection of both doses of the vaccine and subsequent boosters. therefore, those who have recovered from covid-19, regardless of seropositivity, are still advised by health bodies such as the cdc to seek vaccination to prevent future reinfection and to limit future potential spread of covid-19. seroconversion in hepatitis b the typical seroconversion timecourse for hepatitis b seroconversion plays a major role in the diagnosis and treatment of hepatitis b infections. as in other viral infections, seropositivity indicates that an individual has a sufficiently high concentration of antibody or antigen in the blood to be detectable by standard techniques. while assays for other infections such as covid-19 and hiv primarily test for seroconversion of antibodies against antigens, assays for hbv also test for antigens. the standard serology panel for seroconversion include hepatitis b surface antigen, hepatitis b surface antibody for igm and igg, hepatitis b core antibody for igm and igg, and hepatitis b e-antigen. in the typical disease course for hepatitis b, the individual will first seroconvert for hepatitis b surface antigen (hbsag). while some can convert within one week, most individuals take about four weeks after initial infection to convert. anti-core antibodies (anti-hbc) are the first antibodies produced by the body, first in short-term igm (anti-hbc igm), and subsequently in long-term igg; while levels of igm anti-hbc will peak around sixteen weeks after exposure and fall within about seven to eight months, igg anti-hbc will remain detectable in the serum as a sign of chronic infection for years. igm anti-hbc concentration will fall regardless of whether or not the individual clears the infection. the window period for hbsag/anti-hbs testing occurs as concentration of hbsag falls and before the body develops anti-hbs antibodies, lasting approximately six to eight weeks in most individuals. during this time, serology assays can test for total anti-hbc. levels of anti-surface antibody (anti-hbs) generally become detectable after thirty-two weeks and peak around thirty-six to forty; the production of anti-hbs antibodies indicates imminent resolution of the hbv infection. anti-hbs concentration falls as the infection resolves but does not serorevert completely, and anti-hbs igg remains positive for years as a sign of immunity. hepatitis b e-antigen (hbeag) is a sign of current infectivity. an individual who is seropositive for hbeag can infect others. an individual who is infected with hbv and who never becomes seropositive for hbeag can likewise be infective, because not all hbv infections produce hbeag. for most individuals, those who seroconvert positive for hbeag during their disease course and subsequently serorevert negative as their infection progresses are no longer infective. seroreversion from hbeag is thus used as one marker of resolution of infection. on a serological assay, the presence of hepatitis b surface antigen (hbsag) indicates an individual with a currently active hepatitis b infection, whether acute or chronic. the presence of core antibody (anti-hbc) indicates an individual with an infection in general, whether