American doctors tested thousands of patients who recover from COVID-19. Almost all who have a PCR test showed positive results, after recovery had antibodies against SARS-CoV-2. The study is published on the website of preprints medRxiv.
Specialists Medical school at mount Sinai in new York decided to find out how to form antibodies to the virus SARS-CoV-2 those who had COVID-19. They analyzed data on 1343 patients of whom 624 coronavirus was confirmed by PCR tests, and the rest of 719 diagnosis COVID-19 — put on set of symptoms. The absolute majority of the disease proceeded in a simple way, not requiring hospitalization. The symptoms lasted from one to 67 days.
Patients in the very early new York flash, tested at the end of March — beginning of April. They took blood plasma for antibodies, and also checked whether there is still viral RNA in smears from the nasopharynx. To test for IgG antibodies to the virus SARS-CoV-2 used the method of enzyme immunoassay developed in Medical school mount Sinai hospital and approved by the FDA.
According to the test results in 57 percent were found to have a high titer of specific antibodies IgG, five percent — low titer antibodies, and 39 percent of patients antibodies was not detected.
While almost all (99 percent) of patients with initially positive PCR test were detected specific antibodies to the coronavirus, and of those whom the diagnosis has severe symptoms — only one third.
According to the authors, the time of appearance of antibodies varies widely. The average time to the appearance of high titer antibodies is 24 days from the onset of symptoms, or 15 days after the end of symptoms. Reduced if the IgG titre over time, the researchers in this study did not analyze.
The researchers also found that about 20 percent of patients PCR remains positive even after the disappearance of symptoms. Record persistent PCR positivity was 43 days from the onset of symptoms, or 28 days after their disappearance. However, the authors note that the diagnosed virus RNA in specimens from the nasopharynx does not necessarily mean that the virus retains its viability.
The formation of high titer antibodies, according to the study, took at least three weeks. As a rule, a large number of antibodies were observed in those with longer symptoms and who have passed more time after their disappearance.
The results indicate high reliability of the PCR tests, which, according to the authors, should remain the main method of primary diagnosis COVID-19. Thus, a majority of PCR testing should be conducted no earlier than three to four weeks after the onset of symptoms and not earlier than two weeks after their disappearance.
The researchers conclude that in the majority of patients with PCR confirmed coronavirus few weeks after recovery antibodies, however, how long they persist in the body, the authors can not say yet. It is known that antibodies to SARS-CoV-1 and MERS-CoV over time, disappear pretty fast.