Q: What are antibody (serological) tests?
A: Serological tests detect antibodies in the blood generated during the immune response to a specific infection, such as COVID-19. They are different from tests such as PCR that detect the virus that causes COVID-19. Many new serological tests for COVID-19 have been developed; however to date only four have been authorized by the Food and Drug Administration (FDA). Some companies are falsely claiming their serological tests have been approved by the FDA or that they can diagnose COVID-19 infections. The Idaho Division of Public Health discourages the use of unauthorized serology-based assays for diagnosis of COVID-19 or determining someone’s infectious or immune status. Rapid serological tests are not recommended for COVID-19 diagnosis. They detect antibodies generated over time as the body responds to an infection, typically in the second week after a person develops symptoms. People in the early stages of COVID-19 might test negative despite being highly infectious. Additionally, some tests might give a false positive result because of past or present infection with other types of coronaviruses. False positive results are also more likely when the percentage of the population with the disease is low. The Idaho Division of Public Health discourages persons who have a positive serology test from relaxing the precautions such as social distancing that are recommended for all Idahoans to prevent spread of coronavirus, and strongly discourages employers form relaxing the employee protections for an employee solely based upon a positive serology test. The immune response to SARS-CoV-2 (the virus that causes COVID-19) infection is not well understood. It is not known whether the antibodies detected by serological assays provide immunity to reinfection.
Q: What is the difference between IgM and IgG? What does it mean if I am positive for one but not for the other?
A: IgM antibodies are produced in the early stages of an infection, whereas IgG antibodies generally do not begin to appear until 7 to 10 days after infection. Testing positive for IgM only, or both IgM and IgG suggests you might have a current or recent infection with the SARS-CoV-2 virus. Testing positive for IgG only suggests that you might have had a previous or recent infection with the SARS-CoV-2 virus.
Q: If a person’s blood sample tests negative using a serological test, does that mean that the person does not have COVID-19?
A: Not necessarily. The person might be in the early stages of COVID-19 infection and has not developed enough antibodies to be detected by a serological test. Results from antibody testing alone are not enough to determine whether someone is infected with SARS-CoV-2. If a person’s blood sample tests positive using a serological test, does this mean that this person is immune to COVID-19? We do not know yet whether people who test positive by a serological test are immune to COVID-19.
Q: I was tested and told I have antibodies to COVID-19. How long will they last?
A: It is not known how long antibodies will last following COVID-19 infection.
Q: How do we know if someone who had COVID-19 is still infectious?
A: Antibody tests do not tell us whether a person is infectious. The CDC has issued symptom-based guidance for determining when a person with confirmed or suspected COVID-19 can be released from isolation, meaning that they are no longer considered infectious. These criteria are as follows: at least 10 days after illness onset, no fever, and symptoms have improved for 72 hours.
Q: What does it mean if I test positive for COVID-19 using a serological test?
A: A positive serology test means that you might have antibodies to the virus that causes COVID-19, indicating that you were infected by the virus that COVID-19 in the past or might be currently infected, depending on the type of antibodies detected. However, there may be a significant chance that a test can give the wrong result, called a false positive, because of cross-reacting antibodies from previous infections such as those caused by other human coronaviruses.
Q: Is it safe to take care of my elderly parents without wearing a mask or face covering?
A: A test for antibodies does not tell you whether you currently have the COVID-19 virus. Cloth masks and face coverings are recommended to reduce the risk of potential spread to others.
Q: Will DHW or the local public health districts be issuing immunity passports?
A: No. Currently, there is no way to tell whether someone is immune to COVID-19. It is not known whether people who have recovered from COVID-19 are immune from reinfection.
Q: If I test positive on an antibody test, do I still need to get vaccinated when a vaccine is available?
A: It is not known whether antibodies detected using serology tests protect against future COVID-19 infections or for how long that protection might last. Guidance on who should get vaccinated will be provided when there is a licensed COVID-19 vaccine available as this will depend on several factors such as the type of vaccine.
Q: Where can I donate my plasma so other people can benefit from my antibodies?
A: The Red Cross has partnered with the FDA to identify eligible people who have recovered from COVID-19 to donate plasma. See the Red Cross website for more information: https://www.redcrossblood.org/donate-blood/dlp/plasma-donations-from-recovered-covid-19patients.html. Vitalant is collecting plasma from people who have recovered from coronavirus to help COVID-19 patients. Vitalant does NOT test for COVID-19, SARS-CoV-2 or any antibodies to the infection. Do not donate blood if you are sick.