What are the tests to find out if I've ever had COVID-19?
Text updated on 2020-09-20
Following a viral infection, the body protects itself with an immune response, involving the production of antibodies. Even when the virus has been defeated and eliminated, the antibodies persist in the blood and can be detected by a so-called serological test. However, we don't know how effective this protection is!
The serological test is used to find out if you have ever been infected with the SARS-CoV-2 coronavirus. A serologic test is a blood test to determine if a person has been previously exposed to a particular pathogen by examining their current immune response. Serological tests can provide information about the spread of disease in a population by identifying individuals who have developed antibodies to the virus. The results of these tests are available between 10 minutes and 5 days. Several highly reliable tests have been developed.
Serological tests measure the presence of antibodies in blood serum and, thus, analyze the antibody composition in the blood. They are increasingly in demand to quantify the number of people who have been infected, including those with mild or no symptoms, or those who have already recovered. A positive serological test does not mean that a person is contagious.
Serological tests differ from RT-qPCR tests, currently used worldwide to diagnose COVID-19 cases, which only indicate the presence of viral material during infection but not whether a person has been infected and subsequently recovered.
Antibodies against the virus appear within a few days. We lack the hindsight to understand the speed of the antibody response as a function of the severity of COVID-19 disease.
Having antibodies against the SARS-CoV-2 virus doesn't necessarily prevent future infections. See the question Can we catch COVID twice?. We don't have enough hindsight to know how long the immune protection lasts. So we must be careful.
YES, the serological test is a reliable test.
NO, a positive test doesn't mean you're contagious.
A positive test suggests immunity, but there is no certainty about the degree and duration of protection.
John Hopkins University Synthesis on Serological Testingdeveloped mainly by the United States, China, South Korea, Singapore, Germany, and England.
Detection of SARS-CoV-2 viruses in people who have already been infected and developed COVID-19 in Korea: Observations on patients in South Korea show that some patients already infected and with antibodies against the virus may re-develop the disease COVID-19 and present viral material in their nasopharyngeal secretions again. It is not yet clear at this stage whether the patients have been re-infected or have never really cleared the virus.Lan, L., Xu, D., Ye, G., Xia, C., Wang, S., Li, Y., & Xu, H. (2020). Positive RT-PCR test results in patients recovered from COVID-19. Jama.
Antibody persistence in MERS disease.Payne, D. C., Iblan, I., Rha, B., Alqasrawi, S., Haddadin, A., Al Nsour, M., ... & Tamin, A. (2016). Persistence of antibodies against Middle East respiratory syndrome coronavirus. Emerging infectious diseases, 22(10), 1824.
Re-infection with SARS-CoV-2 in 3 macaques one month apart does not lead to a relapse.Bao, L., Deng, W., Gao, H., Xiao, C., Liu, J., Xue, J., ... & Qi, F. (2020). Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. bioRxiv.
Duration of antibodies for SARS-CoV-1 induced disease.Wu, L. P., Wang, N. C., Chang, Y. H., Tian, X. Y., Na, D. Y., Zhang, L. Y., ... & Liang, G. D. (2007). Duration of antibody responses after severe acute respiratory syndrome. Emerging infectious diseases, 13(10), 1562.
Characteristics of antibody responses to SARS-CoV-2 in patients.Zhao, J., Yuan, Q., Wang, H., Liu, W., Liao, X., Su, Y., ... & Qian, S. (2020). Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019. Clinical Infectious Diseases.
Characteristics of neutralizing antibodies to SARS-CoV-2 in patients.Wu, F., Wang, A., Liu, M., Wang, Q., Chen, J., Xia, S., ... & Jiang, S. (2020). Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications.
Description of the high-quality Pasteur serological tests: Seroconversion and neutralization of the coronavirus by antibodies occurred 5 to 14 days after the onset of symptoms, confirming previous studies.Grzelak, L., Temmam, S., Planchais, C., Demeret, C., Huon, C., Guivel, F., ... van der Werf, S. (2020). SARS-CoV-2 serological analysis of COVID-19 hospitalized patients, pauci-symptomatic individuals and blood donors. medRxiv, 2020.2004.2021.20068858. doi:10.1101/2020.04.21.20068858