In the last few days, there have been reports of recovered COVID-19 patients testing positive a second time. Since the exact behaviour of the novel coronavirus is still being studied, immunity against it is not fully understood.
For instance, previous coronavirus outbreaks have been inconsistent: a study on the coronavirus that caused MERS revealed that patients are unlikely to get re-infected within a short duration of the original infection; but, after the SARS outbreak, cases of relapse that were reported.
Theoretically, various factors can cause relapse in patients recovered from COVID-19. SARS-CoV-2, the virus that causes COVID-19, is like viruses that cause any other flu. Therefore, there is always a probability of mutation as in the case of influenza viruses. The mutation, theoretically, can make an individual vulnerable to reacquire the COVID-19 infection.
Patients who test positive for COVID-19 develop protective antibodies. Theoretically, there can be a relapse even in patients who have antibodies. At this stage, it is not fully understood as to how the long the antibodies provide protection against the viral infection.
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Also, in the absence of any vaccination, it is not known whether the immunity acquired by the persons is permanent. Another scenario that can lead to relapse is when immunity is compromised, if the patients have underlying conditions and if they are dependent on immunosuppression drugs.
Experts also have pointed out that a “false negative” RTPCR test — the RNA test being conducted to diagnose COVID-19 infection — can lead to a patient testing positive a second time after testing negative in between. There have reports from Spain about imported RNA test kits giving inaccurate results.
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