The COVID-19 epidemic continues to spread, with more than 300,000 confirmed cases worldwide and more than 250,000 outside China. Recently, clinical studies have reported some cases of detection and return to positive cases after discharge. Some people believe that COVID-19 may become a chronic disease with long-term infection, and the epidemic situation may also be “long-term.”
Several experts interviewed by Xinhua News Agency pointed out that there is no clear evidence to support this speculation, but long-term monitoring of patients with rehabilitation should be strengthened and close attention to possible changes. We should also be alert to the possibility that COVID-19 will become a seasonal infectious disease and strike again in autumn and winter.
There is no clear evidence of the “long-term” epidemic
Relevant experts believe that there is no obvious evidence of chronic infection from the structure of COVID-19 virus and animal experiments, but since the knowledge of the virus is still in its infancy, there may be new discoveries in the future.
From the perspective of virus genome structure, the virus cannot be integrated into the human chromosome and carried for life. There is speculation that COVID-19 will become a chronic disease like Hepatitis B. Kazuo Kitato, a professor of virology at Nagasaki University in Japan, said that covalently closed circular DNA (cccDNA) enables hepatitis B virus to cause continuous infection in the human body and cannot be eliminated. However, no region that can synthesize cccDNA has been found in the genome structure of the COVID-19 virus, and long-term infection is unlikely. However, the possibility of COVID-19 virus infecting liver cells and causing hepatitis cannot be ruled out.
Some people also worry that patients with COVID-19 will be infected with drugs and take their medicines for life like AIDS patients, and experts believe that there is no basis.
“After HIV RNA is reverse transcribed into DNA, it will integrate into the human genome and cause chronic infection. Cells with HIV DNA integrated are called ‘virus reservoirs’, and anti-Mill drugs cannot act on virus DNA that has been integrated into human cells. Therefore, once the drug is discontinued, the ‘virus storage’ will re-release the viral DNA and cause the virus to rebound. “Said Wang Yuge, a research scholar at the National Institutes of Health and an AIDS expert.
It can be seen that the “repository of viruses” is the key to causing chronic infection, but the positive-strand RNA of the coronavirus does not undergo reverse transcription integration, and viral RNA does not enter the nucleus and does not form a “repository”. The immune system of most people with COVID-19 recovery will eliminate the virus once it has cleared the virus. “There is no evidence that COVID-19 virus can escape the host’s immune response and form low-level slow replication.”
In addition, animal experiments have also proven that antibodies can be produced after infection with the COVID-19 virus to resist secondary infections.
“Six human coronaviruses (excluding COVID-19 virus) have appeared, and the first four have evolved into common cold viruses instead of causing chronic infectious diseases, which will eventually be cleared from the body by the immune system.” It is said that the long-term carrying of COVID-19 virus may be related to individual immunity.
However, Mark Harris, a professor of virology at the University of Leeds, believes that although coronaviruses often cause shorter-term, self-limiting infections, there are studies in the literature that document persistent infections in animals (mainly bats), and so they Follow-up studies should be closely followed in patients with positive symptoms.
Patients have multiple causes for reyang
So why do Fuyang patients appear? Experts believe that it may be that the virus in the patient’s body is not completely removed when discharged, coupled with the sensitivity and sampling of nucleic acid reagents, it is prone to “false negatives”.
Wang Yuge said that COVID-19 virus is a lower respiratory tract virus, and the nasopharyngeal swab sampling test currently used may not be accurate and prone to “false negatives”. If the patient happens to be at a low level of virus replication, nasopharyngeal swab sampling is difficult to detect the virus and will be misjudged as “healed.” Hiroshi Kitato also believes that because there are no antiviral drugs, the virus may not be completely removed from the body when discharged, and Fuyang is “the virus reignites in the body and the viral load increases again.”
The British “The Lancet” magazine previously published a paper by the Cao Bin team of the China-Japan Friendship Hospital showed that among 137 discharged patients, the median period of virus shedding was 20 days, up to 37 days. Wang Yuge said that this is in line with the characteristics of an acute viral infectious disease, that is, the onset quickly, and the patient eventually recovers or dies. However, due to the long period of virus shedding, the virus level in the body will fluctuate repeatedly during this period, and the disease will also repeat. If a patient has an innate immune deficiency, antibodies may never be produced.
Kitasato also proposed another possibility. Because the COVID-19 virus is an RNA virus, it has a strong ability to mutate. The mutated part may cause the nucleic acid to be undetectable. At the same time, the neutralizing effect of the antibody is avoided, and the virus escapes immunity. The attack and removal of the system does not rule out the possibility of Fuyang.
Professor Zhang Kang of the Macau University of Science and Technology School of Medicine said that it is also possible that after a negative respiratory tract test, the patient still had COVID-19 virus in his stool and intestines, and later infected the respiratory tract. His team recently published research in the British journal Nature Medicine to give theoretical support, but further verification is needed.
Experts recommend that patients be “dual-tested” for nucleic acids and antibodies before discharge to avoid “false negatives”. Hiroshi Kitato said that if the nucleic acid turned negative and an IgG antibody that was a marker of previous infection appeared and the imaging lesions of the lungs disappeared, it could be said that it was basically cured.
Because the scientific community still lacks sufficient understanding of the COVID-19 virus, experts believe that more in-depth virus biology research should be carried out to conduct long-term health monitoring of discharged patients, especially dynamic monitoring of IgM antibodies suggesting acute infection to prevent resuscitation. The patient still has infectious or other changes. It is also important to prevent COVID-19 from becoming a seasonal epidemic and make a comeback in autumn and winter.
“In any case, developing an effective vaccine is the best prevention and control measure, and it is also an urgent problem that needs to be solved.” Saito Kitato said that the COVID-19 virus may produce multiple mutations like the influenza virus, and it is necessary to target in the future. Development of multiple vaccines for different subtypes of viruses.