![]() Antibody testing may be useful to support the diagnosis of COVID-19 illness or complications of COVID-19 in the following situations: During this interval, the sensitivity of detecting infection using NAAT or antigen detection testing decreases and the sensitivity of serologic testing increases. Persons suspected of having COVID-19 who test positive by direct viral detection methods for SARS-CoV-2 (e.g., NAAT or antigen detection tests) typically begin to develop measurable antibody 7–14 days after illness onset, and by 3 weeks most persons will test positive for antibody. The clinical applicability of semi-quantitative tests has not been established. ![]() Although the surrogate neutralization test exhibits correlation to a plaque reduction neutralization test, the clinical or public health applicability has not been established. Plaque reduction neutralization assays are considered the gold standard for detection of neutralizing antibodies, but require cells, infectious virus, and are difficult to standardize. Detection of persistent antibodies varies by the test used.įDA has issued an EUA for surrogate neutralization tests, which are qualitative binding assays that detect antibodies that block the interaction between the virus and the cellular virus receptor (ACE-2) without using cells or infectious virus.IgM antibody can persist for weeks to months following infection, though its persistence appears to be shorter than IgG’s therefore, detection of IgM could suggest relatively recent infection.Therefore, assays that measure total antibody or IgG could have higher sensitivity than IgM assays as more time passes since a person’s last infection. IgG levels appear to decrease more slowly over time than levels of other classes of antibody.Īntibody tests with very high sensitivity and specificity are preferred since they are more likely to exhibit high positive (probability that the person testing positive actually has antibodies) and negative predictive values (probability that the person testing negative actually does not have antibodies) when administered at least 3 weeks after the onset of illness.Īdditional considerations when selecting an antibody test include: The list of qualitative and semi-quantitative SARS-CoV-2 antibody tests granted an EUA by the FDA can be found on FDA’s website. Everyone, regardless of whether they have antibodies or not, should still take steps to protect themselves and others, including staying up to date on vaccination.Ĭhoice of antibody test and testing strategyįor all clinical and public health purposes, it is recommended to use one of the numerous antibody tests for SARS-CoV-2 that have been authorized by FDA. Antibody tests are not used for diagnosing a current case of COVID-19. ![]() Even after a person’s antibodies wane, their immune system may have cells that remember the virus and that can act quickly to protect the person from severe illness if they become infected.Īntibody tests can detect the presence of these antibodies in serum within days to weeks following acute infection or vaccination. As their antibodies wane, a person may become more vulnerable to SARS-CoV-2 infection. For many diseases, including COVID-19, antibodies are expected to decrease or “wane” over time. It is important to remember that some people with antibodies to SARS-CoV-2 may become infected after vaccination ( vaccine breakthrough infection) or after recovering from a past infection ( reinfection). Antibodies are just one part of a persons’ immune response.Īntibodies to severe acute respiratory syndrome coronavirus 2 ( SARS-CoV-2), the virus that causes COVID-19, can be detected in the blood of people who have recovered from COVID-19 or people who have been vaccinated against COVID-19. How long this protection lasts can be different for each disease, each person, or influenced by other factors. Even if a person does get sick, having antibodies can protect them from getting severely ill because their body has some experience in fighting that disease.
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