The COVID-19 epidemic is ignited by the global spreading of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) , which has been the center of scientific research for an effective treatment since the beginning of the outbreak. SARS-CoV-2 is a betacoronavirus, which as a RNA virus has a high mutation rate, correlating to its strengthened virulence .The very latest study on the SARS-CoV-2 reinfection case released by HKU undermined the viability of the herd immunity constructed by natural infection and vaccination , showing that the virus will likely be circling within human populations. And, on the other hand, this report made us reconsider the necessary approaches during vaccine design and against SARS-CoV-2, including vaccination for recovered patients .
The reinfection case was supported with genetic evidence which differentiated it from the prolonged first episode infection , and this may imply that future vaccines may not provide a very lasting immunity against SARS-CoV-2. In contrast, as denoted by Le Bert et al. , serological samples from patients who recovered from SARS-CoV-2 and SARS (SARS-CoV) years ago, and those who were never exposed to SARS and SARS-CoV-2, displayed the presence of SARS-CoV2-specific T cells. The T cell response mounted differed in two patient groups, where the ORF1-specific T cell responses were greater in the patients with no infection history, while the structural protein specific T cell responses were preferentially detected in patients who recovered from either SARS . The action of cross-reactive T cells can be explained by the fact that, different strains of coronaviruses share sometimes highly conserved genetic and structural components (see Figure.1), for instance, the ORF1 region which encodes non-structural proteins (NSPs), accounting for two thirds of the virus genome . In addition, structural proteins, in the above study the N proteins, also have a considerable degree of homology among betacoronaviruses . Accordingly, it is supposed that patients who were never exposed to the SARS-CoV-2 acquired the pre-existing from previous infection with homolog commoncold coronaviruses like HCoV-OC43, HCoV-HKU1, HCoV-NL63 and HCoV-229E ; this might explain the fiercely varied severity seen in the patient population [3,5]. Through the understanding of the underlying mechanisms that determine the severity of the SARS-CoV-2 infection is vital for the control of the disease, as people with distinct levels of pre-existing T cell memory may mount immune response of different strength and speed ; it may also shed light on the design of novel vaccines for SARS-CoV-2.
Figure.1. Sequence Map of SARS-CoV-2 (Taken from Le Bert et al., SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls., 2020, Fig.1)
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