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Enlarge / Medical staff wearing personal protective equipment (PPE) as a precautionary measure against the COVID-19 coronavirus approach Lei Muk Shue care home in Hong Kong on August 23, 2020. Getty | May James

A healthy, 33-year-old man in Hong Kong is now the first person in the world confirmed to have been reinfected by the pandemic coronavirus, SARS-CoV-2—which has currently infected more than 23 million people worldwide.

The mans first infection was in late March. He reported having a cough with sputum, fever, sore throat, and a headache for three days before testing positive for the virus on March 26. Though his symptoms subsided days later, he was hospitalized on March 29 and remained in the hospital until April 14, when he tested negative for SARS-CoV-2 in two tests taken 24-hours apart.

About 4.5 months later, the man tested positive for the virus again. This time, his infection was caught during entry screening at a Hong Kong airport, as he returned from a trip to Spain, via the United Kingdom, on August 15. Though he had no symptoms, he was again hospitalized. Clinical data showed he had signs of an acute infection, but he remained asymptomatic throughout his time in the hospital.

Researchers decoded the entire genetic sequences of the SARS-CoV-2 viruses isolated from the man in both infections and found that his two infections were caused by clearly different strains of the coronavirus. The first strain looked much like SARS-CoV-2 strains collected in April and March in the United States and England. The second was closely related to strains collected in England and Switzerland in July and August. Overall, there were 24 genetic differences between the two infecting viral strains, including significant differences in the code for the infamous spike protein.

Hong Kong researchers report the case August 24 in a scientific study that was accepted, but not yet published, by the journal Clinical Infectious Disease. A draft version of the accepted study was released to Ars by the University of Hong Kong and a PDF is available HERE. The PDF does not include the studys three figures, but the University released a phylogenetic tree (Figure 2), which you can see HERE. Ars has requested the other figures and will update this text when they become available.

Dont panic

With tens of millions of cases around the globe that have accumulated over eight months, cases of reinfection are not surprising—or even necessarily concerning. Studies so far have suggested that immune responses to SARS-CoV-2 can be variable, meaning some people may develop stronger, more protective immune responses than others. There is mounting data suggesting that some immune responses can be completely protective against reinfection—at least for some period of time. From this new study, its also rather encouraging that the mans second infection was even milder than the first—it was completely asymptomatic, in fact—hinting at helpful immune responses specifically against SARS-CoV-2.

Though there have been other, more anecdotal reports of reinfection, those have not been confirmed as this one has, with full genome sequencing and other data. And, while documenting this case is certainly important, it still leaves all of the most significant questions about SARS-CoV-2 immunity unanswered.

That is, we still dont know what levels of immune responses are necessary to prevent reinfection and/or disease. We still dont know what proportion of people develop such protective immune responses after an infection. And we dont know how long any protective immune responses last in most people.

Several studies have suggested that antibody responses to SARS-CoV-2 can wane after a two- to-three month period. Antibodies are the Y-shaped proteins that circulate in the body after an infection and are specifically designed to detect different bits of SARS-CoV-2. When they do, they can hail immune responses or even neutralize the virus completely, potentially thwarting another infection. Levels of antibodies naturally wane after an acute infection, but some researchers have expressed concern that anti-SARS-CoV-2 antibodies seem to decline more quickly than expected. As such, some have speculated that protective immune responses against SARS-CoV-2 may resemble those seen from infections by other human coronaviruses, ones that cause common colds. Infections with those garden-variety coronaviruses typically only produce immunity that lasts on the scale of months rather than years or decades, and reinfections are common.

But again, all of this is still speculative. We dont know what levels of antibodies are necessary to protect against a second SARS-CoV-2 infection, let along how long those levels last. So, we dont know if any of the declines measured are meaningful. Moreover, antibodies are not the only protective immune response to consider; there are also responses from immune cells, called B cells and T cells, that can be protective as well.

Wrinkles and limitations

Its also important to note that the case report on the confirmed reinfection has some interesting wrinkles and important limitations. For one thing, the researchers point out that the two strains of SARS-CoV-2 that infected the man had significant differences in their spike proteins.

Generally, each SARS-CoV-2 virus has many copies of spike protein jutting out from its spherical viral particle, much like the spikes of a sea mine. These protruding barbs can seize human proteins called ACE2 receptors, which stick out from the surface of some human cells. When this interaction occurs, it essentially opens to door to a SARS-CoV-2 viral infection into the ACE2-donning human cells.

Because the SARS-CoV-2 spike protein is so prominent on the viral particles, anRead More – Source

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