In this study, the IgM and IgG antibodies associated with SARS-CoV-2 are analyzed from 221 COVID19 positive patients. These antibodies can give insight on the diagnosis, cause of the virus, and course of the virus. The concentration of the IgM antibodies was highest between day 16 and 18 after the first day of symptoms. IgG antibodies peaked between days 19 and 21. The IgG concentration was much higher in severe cases compared to other cases of COVID19. Just over 50% of patients who discharged tested positive for SARS-CoV-2 RNA after a nasal swab. The patients who tested positive for the RNA had lower levels of IgG than patients who tested negative for RNA. Two weeks after discharge, IgG and IgM levels still decreased for both RNA positive and negative patients. This study concludes that the antibody concentration does not affect the course or the outcome of the virus. Immunity to the virus by the presence of the IgG antibody is still unclear and needs further investigation.
SARS-CoV-2 is one of seven coronaviruses that can infect humans. Out of the coronaviruses, SARS-CoV-2 causes more severe symptoms. When a patient is infected with SARS-CoV-2, the immune response is activated. The specific immune response produces IgM and IgG antibodies. IgM antibodies develop the fastest and tells us there is current infection. IgG antibodies are the most common antibodies of the immune response. IgG antibodies also develop the slowest. The presence of IgG can show that a patient has recovered. Testing for both IgM and IgG can tell physicians if you have COVID19 and how long you have had it. IgM testing is already used as diagnosis criteria in China. But, the ability of IgG levels to show if we have long term immunity has not been confirmed. Some patietns test positive for viral RNA after they are discharged and feeling better. The relationship of IgM and IgG antibodies to these patients is also unknown.
211 confirmed COVID-19 patients in China were included in this study, with a range of mild and severe cases. IgG and IgM antibody testing was done every three days after the onset of symptoms. Antibodies were analyzed for concentration differences between mild and severe patients. Some patients were positive or negative for IgG or IgM upon admission to the hospital. Throughout Days 16-21 age, other chronic diseases, fever, white blood cell count, pulmonary inflammation index and other various factors were all looked at in association to the presence or absence of IgG and IgM antibodies. Patients were discharged after meeting the criteria of the Guidelines for the Diagnosis and Treatment of Novel Coronavirus Infection by the National Health Commission. The antibodies were detected by using fluorescence and luminescence techniques. Using this analysis, a value of less than 1 is considered negative for the antibody.
Patients who were older, had diabetes, cardiovascular diseases, or chronic obstructive pulmonary disease were more likely to have a more critical illness. The concentrations of IgG and IgM peaked from 19-21 days after symptom onset. After the peak, IgM decreased slowly while IgG stayed high. The IgM levels were the same between mild and severe COVID-19 cases, but the IgG levels were much higher in those with severe cases. A higher pulmonary inflammation index was found with patients who tested negative for IgM. For people who tested positive for IgG and IgM from 16 to 21 days after symptom onset, the antibody levels were not associated with length of hospital stay, duration of positive virus detection, duration of fever, changes in the pulmonary inflammation index, or outcome of the virus. Of the 74 patients who were discharged during the study, 52.7% of them tested positive for SARS-CoV-2 RNA. The positive RNA patients had lower IgG concentrations after discharge, but very little change in IgM after 7 days. The entire group of discharged patients experienced a drop in the level of IgG, IgM, any white blood cells after 14 days post discharge.
Despite the findings of this study, there were two patients who did not develop IgM or IgG antibodies throughout the virus. So, the antibody testing is a good indicator of the course and onset of the virus, but should not be used to rule out SARS-CoV-2. RT-PCR is another diagnosis test that should be used if the patient is negative for the IgG or IgM antibodies. Since a decrease in IgG after discharge was seen, we cannot be sure that IgG antibodies give us long term immunity against SARS-CoV-2. More research should study if IgG can give us long term immunity. This study could be helpful in developing a vaccine because it has shown the timeline of IgG and IgM levels throughout the virus. The higher pulmonary inflammation index in patients who were negative for IgM shows that people with a slower immune response have more severe respiratory symptoms. Still, this supports that the best available current treatment is still human immune activity. Other studies have found that IgG against the spike protein of COVID-19 is associated with lung inflammation and injury. So, the possible protective effect of IgG antibodies and lung damage needs to be investigated. Some studies have suggested treating critical COVID-19 patients with serum of recovering COVID-19 patients, but this also needs more investigation since there have been mixed findings about the harmful organ damage and protective effects of IgG antibodies in patients with SARS-CoV-2.