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Reinfection vs relapse

Among the many mysteries and unknown variables that surround SARS-CoV-2 is the role of antibodies and immunity in preventing infection and, in this case, re-infection. While plasma extracted from recovered patients is being used as a treatment therapy worldwide, scientists and doctors have been straightforward in stating that they do not understand how long this immunity lasts. Research has shown that antibody levels start decreasing after a certain period of time. This naturally implies that it may very well be possible for a person to recover from COVID-19, only to be reinfected when the antibodies in their blood start decreasing to the point of ineffectiveness. Till now this has been a matter of speculation, a scenario that experts see as likely but has not had any recorded cases to establish the fact beyond a doubt. This changed recently as researchers in Hong Kong reported that a 33-year-old male has been confirmed as once again being COVID positive after being discharged from a hospital in April. The man tested positive after returning from Spain via Britain. It must be noted that researchers confirmed the reinfection beyond a doubt by carrying out tests that showed that the man had contracted a different Coronavirus strain from the one he had contracted previously and this time around he was asymptomatic. After the confirmation, two more European patients — one in the Netherlands and the other in Belgium were also stated to have been reinfected by the Coronavirus. As was the case with the Hong Kong reinfection, the two European reinfections were confirmed as 'true' reinfections only after being confirmed to see whether the two instances of the virus are different.

The idea of the virus flaring up after recovery is otherwise not uncommon. In May, Chinese experts noted that between 5-15 per cent of the patients who were being discharged would test positive once again later. Doctors in India have confirmed many cases as well where patients tested positive after being discharged. But in such cases, it was hard to differentiate whether the resurgence was a true reinfection or simply the original infection coming back with a vengeance. Why this happens is also a matter of much mystery. One of the theories being forwarded is that the virus still exists in some measure in the patient's lungs even after recovery. A weaker immune system naturally makes such resurgence likely. Proving a reinfection versus a relapse has not been an easy task Early on, it was realised that the current standardised test for COVID does not differentiate between a 'live' and 'dead' virus. A study in South Korea showed that many reports of reinfection in recovered patients were just tests showing false positives after detecting the dead virus.

So the obvious question at this point may well be to question what this means for our efforts in developing the vaccine? As with most things regarding the pandemic, there is no easy answer to this. Most experts concede that too little time has passed to make definite statements regarding the nature of antibodies and their role in fighting the virus. While we may have some idea as to how our antibodies decline after a few months, next to nothing is known about how the body's T cells — the mechanism through which long-lasting immunity comes to be — deal with the contagion. The Oxford study is one of the few studies which have tried to assess the role of both antibodies and T cells in keeping recovered patients safe.

For now, it raises the possibility that SARS-CoV-2 may live on in the human population, even after the vaccine is developed. Much like the flu, it may become an endemic disease that requires newer vaccines to be developed and administered each year. Grim undertones aside, most experts agree that this development is scarcely enough to cast clouds of pessimism over hopes of a working vaccine.

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