Post by Admin on Apr 23, 2020 20:51:49 GMT
A new study from Chinese scientists on 130 recovered COVID-19 patients is raising questions about the extent to which people develop immunity to the virus.
The paper — a pre-print that has not been peer-reviewed yet — found that patients produced differing levels of antibodies . Having identifiable coronavirus antibodies in your bloodstream means you've probably built up immunity. But roughly 6% of the patients studied didn't develop any detectable antibodies at all.
"What this will mean to herd immunity will require more data from other parts of the world," Huang Jinghe, the leader of the research team behind the report, said, according to the South China Morning Post.
Interestingly, the levels of antibodies patients produced seemed to correlate with their ages: Middle-aged and elderly recovered patients had higher levels of antibodies. Nine of the 10 of the patients who did not develop detectable levels of coronavirus antibodies were 40 years old or younger.
Finding out more about how antibodies to the virus work will have major implications for both vaccine development and the potential for herd immunity.
The study, from researchers from Fudan University in Shanghai, took blood samples from 175 coronavirus patients who had recovered at Shanghai hospitals and who'd had "mild" symptoms. (Patients with "severe" symptoms were excluded because many had received blood transfusions to treat their illnesses.)
The participants ranged in age from 16 to 68, and the scientists grouped them into three categories: elderly (60-85), middle-aged (40-59), and young (15-39).
They found that the patients developed antibodies around 10 to 15 days after the disease's onset and remained stable afterwards.
The researchers measured the levels of neutralizing antibodies (NAbs) in each patient's blood, and found that recovered elderly patients developed significantly higher levels of antibodies than younger patients did. But there was no difference between the lengths of the patients' hospital stays.
"These results indicated that high level of NAbs might be useful to clear the viruses and helpful for the recovery of elderly and middle-age patients," the authors wrote.
The virus seems to be more fatal for older people. In the US, patients 65 and older are seeing the highest rates of death and serious illness, according to the Centers for Disease Control and Prevention.
In the 10 patients in the study who did not develop detectable antibodies, "other immune responses, including T cells or cytokines, may contribute to the recovery," the researchers wrote.
T cells are a type of white blood cells that aid in immune response, and cytokines are a type of molecule that cells release to fight infections. However, when too many cytokines are released, they cause inflammation — which has reportedly contributed to fatal outcomes in some COVID-19 patients.
Even in patients who do develop coronavirus antibodies, scientists still aren't sure how long they'll last; the virus has not been around long enough to study long-term effects.
Generally, once your body has antibodies to fight off a particular disease, you can't get it again, though some types of antibodies weaken over time. Plus, with viruses that mutate — such as the common cold or seasonal flu — antibodies people build up against one strain aren't effective against others.
Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications
Fan Wu, Aojie Wang, Mei Liu, Qimin Wang, Jun Chen, Shuai Xia, Yun Ling, Yuling Zhang, Jingna Xun, Lu Lu, Shibo Jiang, Hongzhou Lu, Yumei Wen, Jinghe Huang
doi: doi.org/10.1101/2020.03.30.20047365
Abstract
Background The COVID-19 pandemic caused by SARS-CoV-2 coronavirus threatens global public health. Currently, neutralizing antibodies (NAbs) versus this virus are expected to correlate with recovery and protection of this disease. However, the characteristics of these antibodies have not been well studied in association with the clinical manifestations in patients. Methods Plasma collected from 175 COVID-19 recovered patients with mild symptoms were screened using a safe and sensitive pseudotyped-lentiviral-vector-based neutralization assay. Spike-binding antibody in plasma were determined by ELISA using RBD, S1, and S2 proteins of SARS-CoV-2. The levels and the time course of SARS-CoV-2-specific NAbs and the spike-binding antibodies were monitored at the same time. Findings SARS-CoV-2 NAbs were unable to cross-reactive with SARS-CoV virus. SARS-CoV-2-specific NAbs were detected in patients from day 10-15 after the onset of the disease and remained thereafter. The titers of NAb among these patients correlated with the spike-binding antibodies targeting S1, RBD, and S2 regions. The titers of NAbs were variable in different patients. Elderly and middle-age patients had significantly higher plasma NAb titers (P<0.0001) and spike-binding antibodies (P=0.0003) than young patients. Notably, among these patients, there were ten patients whose NAb titers were under the detectable level of our assay (ID50: < 40); while in contrast, two patients, showed very high titers of NAb, with ID50 :15989 and 21567 respectively. The NAb titers were positive correlated with plasma CRP levels but negative correlated with the lymphocyte counts of patients at the time of admission, indicating an association between humoral response and cellular immune response. Interpretation The variations of SARS-CoV-2 specific NAbs in recovered COVID-19 patients may raise the concern about the role of NAbs on disease progression. The correlation of NAb titers with age, lymphocyte counts, and blood CRP levels suggested that the interplay between virus and host immune response in coronavirus infections should be further explored for the development of effective vaccine against SARS-CoV-2 virus. Furthermore, titration of NAb is helpful prior to the use of convalescent plasma for prevention or treatment. Funding Ministry of Science and Technology of China, National Natural Science Foundation of China, Shanghai Municipal Health Commission, and Chinese Academy of Medical Sciences
Competing Interest Statement
The authors have declared no competing interest.