During retesting of patients who have recovered from Covid-19, tests sometimes give a positive result for the presence of the virus in the body – even after the patient has fully recovered and symptoms (if any) have disappeared. Since knowledge of the new virus is still very limited, it took several months for scientists to understand how the retest could produce such a result and what conclusions should be drawn from it.
Does this mean that the transmitted disease does not provide immunity to those who have recovered, and therefore it is possible to be infected with Covid-19 multiple times? Can a person remain contagious after full recovery, and if so, how long will they pose a risk to others?
There is still no clear answer to the first question. We know that a person develops specific immunity after a transmitted disease, but we can only speculate how long recovered patients remain immune to the coronavirus. Some diseases (such as measles or chickenpox) provide immunity for life, while others (such as hepatitis A, yellow fever, and others) provide immunity for about 10 years, and viruses such as seasonal flu do not leave much specific immunity. In the case of Covid-19, however, immunity should last for at least a year or two (according to more closely related viruses), making it unlikely that patients will become infected again.
The second question seems to have been answered by South Korean scientists: recovered patients are not contagious and do not pose a danger. On Wednesday, health experts in the country stated that repeat tests can yield positive results even after the patient has fully recovered due to the presence of inactivated virus fragments in their bodies. On Tuesday, it was reported that in South Korea, tests are still detecting the virus in nearly 300 people who have recovered from Covid-19, while the total number of recovered patients is approaching 9000. However, upon close examination of these analyses, medical professionals found no active viral particles in any of the positive tests performed on those who had recovered.
The fact is that most of the tests used worldwide to diagnose Covid-19 use the polymerase chain reaction method (PCR tests), the purpose of which is to significantly increase the concentration of the virus’ genetic material in order to facilitate its detection in the sample collected.
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In this case, according to the scientists, the tests proved to be very sensitive and reacted not to the virus itself, but to separate fragments of viral RNA that remained in the patients’ bodies and multiplied during the test. “RNA fragments may remain in the cell even if the virus itself is neutralized,” said the statement from the South Korean Central Clinical Committee for the Control of New Diseases. “Most likely, repeated analysis showed the presence of RNA from an already neutralized virus.” However, experts emphasize that the virus is not infectious in such a decomposed state, so these individuals do not pose a danger to others, as it is virtually impossible to reactivate the virus unless Covid-19 causes a chronic infection.
“Unlike other infectious agents such as HIV or hepatitis B, the virus that causes Covid-19 does not penetrate the cell nucleus and does not integrate into the patient’s DNA. Therefore, it does not cause chronic infection,” Oh Myung-dong, head of the committee, assured journalists.
Most experts believe that sooner or later the SARS-CoV-2 coronavirus will infect a significant portion of the world’s population. The Russian service of the BBC answers the most important questions about the SARS-CoV-2 coronavirus.