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新型コロナの感染者、完治後も抗体が弱いとの報告!3割で予想以下 「再感染の恐れ」「免疫は厳しいかも」

新型コロナウイルスについて新たな調査結果が発表されました。

これは中国の研究チームによると、新型コロナウイルスの感染が確認されて治療を終えた患者ら175人分の血液を調査したところ、3分の1の被験者で予想よりも中和抗体の量が少なかったことが判明したとのことです。
当初は新型コロナウイルスに感染して完治すれば、抵抗するための抗体が作られると思われていましたが、全体の3割の退院患者は抗体があまり見られなかったとまとめられています。

抗体が予想よりも少ないことで再感染のリスクもあるとして、いわゆる集団免疫にも疑問を投げ掛けていました。この論文は査読を行っていないことから、あくまでも参考程度の情報だとして、情報の精査が必要だと強調されています。

中国では多数の再感染報告があり、イタリアにおいても治療後に発症したとの報告が何件かありました。仮に新型コロナウイルスの感染後も抗体が中々作られないとすれば、集団免疫論は完全否定される形になると言え、ワクチンや治療薬開発にも大きな影響を与えそうです。

 

Coronavirus: low antibody levels raise questions about reinfection risk
https://www.scmp.com/news/china/science/article/3078840/coronavirus-low-antibody-levels-raise-questions-about

Researchers in Shanghai hope to determine whether some recovered coronavirus patients have a higher risk of reinfection after finding surprisingly low levels of Covid-19 antibodies in a number of people discharged from hospital.
A team from Fudan University analysed blood samples from 175 patients discharged from the Shanghai Public Health Clinical Centre and found that nearly a third had unexpectedly low levels of antibodies.
In some cases, antibodies could not be detected at all.
“Whether these patients were at high risk of rebound or reinfection should be explored in further studies,” the team wrote in preliminary research released on Monday on Medrxiv.org, an online platform for preprint papers.
Although the study was preliminary and not peer-reviewed, it was the world’s first systematic examination of antibody levels in patients who had recovered from Covid-19, the disease caused by the coronavirus, the researchers said.

Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications
https://www.medrxiv.org/content/10.1101/2020.03.30.20047365v1

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.

 

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