The Covid-19 pandemic has undoubtedly taken a huge toll on lives the world over and overwhelmed even the strongest health systems. The only positive thing is the high recovery rate: over 90 percent. The People’s Daily reported that overall recovery rate in Wuhan was 99.2 percent while it was 88.2 percent in severe cases. Skepticism however has been expressed over chances of reoccurrence of infection among the discharged patients. It is assumed that any person who has recovered from pathogenic infections develops antibodies to prevent relapse.
Li QinGyuan, Director of Pneumonia Prevention and Treatment at China Japan Friendship Hospital in China, says the infected do develop antibodies against that virus. But he says it is unclear how long the antibodies remains. The recovery rate in Nepal has been seen encouraging yet the public is in dilemma over reappearance of infection. As of now, three recovered cases in Nepal have again tested positive on Real time Reverse Transcription–Polymerase Chain Reaction (RT-PCR) test during follow-up.
Recovered patients with underlying conditions or weak immune systems may not develop sufficient antibodies to ward off fresh attack from the virus. Relapse is high in patients suffering from diabetes, cancer, cardiovascular diseases, HIV/AIDS, even malnutrition. Even for a person with a strong immune system, it is unclear how long antibodies are at work following the recovery.
The WHO on April 24 said “no study has evaluated whether the presence of antibodies of Covid-19 confers immunity to subsequent infection.” However it has also been reported that like other coronaviruses—‘Severe acute respiratory syndrome’ or ‘Middle Easter respiratory syndrome’ that caused pandemics in 2002 and 2012 respectively)—Covid-19 antibodies persists for longer, probably two to three years. Public health and medical professionals also believe immunity against Covid-19 remains for long period.
No test including RT-PCR is 100 percent valid for confirming Covid-19 infection. Hence patients who have recovered may test positive in follow-up owing to false negative in earlier test. Likewise, there is a chance that patient discharged from the hospital might be falsely diagnosed positive in follow-up test. BMC journal states that sensitivity (true test positive rate) and specificity (true test negative rate) of RT-PCR is 70 percent and 95 percent respectively. It implies that despite having Covid-19 virus, there is 30 percent probability that test results might be negative. In follow up test of the same case, there is chance that patient can be correctly diagnosed positive by RT-PCR machine. Similarly, there is five percent probability of being diagnosed falsely positive in follow-up test after being discharged despite not having Covid-19 pathogens. This is why many countries, including India, mandate at least two tests in 24 hours, with both of them testing negative, to declare that the patients has recovered.
The big flaw of RT-PCR is that although it is good at identifying Covid-19, it cannot differentiate whether the virus is dead or alive. WHO says the person discharged from hospital may test positive in RT-PCR for several weeks but he/she is unlikely to be infectious enough to spread the disease. According to Dr. Oh Myoung-don of Seoul National University Hospital, dead virus can be present in human body long after recovery. So the RT-PCR test can still turn out positive result in this time. To confirm the virus is dead, the collected throat sample can be cultured in laboratory. As the process of culture takes time and calls for viral isolation measures, it may not be feasible during epidemics.
A study in China mentioned that 5-10 percent of the Covid-19 cases there are reinfections. Reactivation of the virus is one reason the cured patient tests positive on RT-PCR during follow-up test. The pathogens tend to be dormant or latent within a cell and hide from immune cells during the stage of viral latency. They don’t cause any illness in this stage and no symptoms are seen. This might ultimately lead medical professionals to believe patients are infection-free and thus discharge them from hospitals, mainly in resource-poor settings. After a certain time, replication and multiplication of the virus leads to RT-PCR test positive result.
Public health experts and virologists have shown increasing concerns over possible mutation, the change in genetic sequence of new coronavirus. Unlike DNA virus, the new coronavirus, which is RNA virus, is more susceptible to change. It can lead to evolution of virus into less or more harmful forms. Severe forms of Covid-19 may worsen the global health crisis as it augments the risk of re-infection of recovered patients despite their antibodies.
There are no in-depth studies to prove recovered patients are immune to Covid-19, while some reports suggest they might be re-infected. Thus the recovered patients should continue to maintain self-isolation, physical distancing, personal hygiene, and taking balanced diet. In addition, they should be under medical surveillance for at least two weeks following ‘full recovery’ and undergo a follow-up RT-PCR test in line with the Good Microbiological Practice and Procedure (GMPP) to avoid any test error.
The author is a graduate in Epidemiology and Bio-Statistics from SRM University, India