Protective immunity after recovery from SARS-CoV-2 infection

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The SARS-CoV-2 pandemic is now better controlled in settings with access to fast and reliable testing and highly effective vaccination rollouts. Several studies have found that people who recovered from COVID-19 and tested seropositive for anti-SARS-CoV-2 antibodies have low rates of SARS-CoV-2 reinfection. There are still looming questions surrounding the strength and duration of such protection compared with that from vaccination.


We reviewed studies published in PubMed from inception to Sept 28, 2021, and found well conducted biological studies showing protective immunity after infection (panel). Furthermore, multiple epidemiological and clinical studies, including studies during the recent period of predominantly delta (B.1.617.2) variant transmission, found that the risk of repeat SARS-CoV-2 infection decreased by 80·5–100% among those who had had COVID-19 previously (panel). The reported studies were large and conducted throughout the world. Another laboratory-based study that analysed the test results of 9119 people with previous COVID-19 from Dec 1, 2019, to Nov 13, 2020, found that only 0·7% became reinfected. In a study conducted at the Cleveland Clinic in Cleveland, OH, USA, those who had not previously been infected had a COVID-19 incidence rate of 4·3 per 100 people, whereas those who had previously been infected had a COVID-19 incidence rate of 0 per 100 people. Furthermore, a study conducted in Austria found that the frequency of hospitalisation due to a repeated infection was five per 14 840 (0·03%) people and the frequency of death due to a repeated infection was one per 14 840 (0·01%) people. Due to the strong association and biological basis for protection, clinicians should consider counselling recovered patients on their risk for reinfection and document previous infection status in medical records.

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Source: Noah Kojima, Jeffrey D Klausner | The Lancet 

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