The cases of COVID-19 recurrence already described in the world show that resistance to SARS-CoV-2 may decline relatively quickly. Surviving the infection does not guarantee permanent immunity. Understanding the pattern of immune memory function is important in assessing the chance of recurring infections.
- What have scientists been able to determine so far about resistance to the coronavirus?
- Data show that the number of SARS-CoV-2 re-infections is increasing. Several hundred such cases have already been reported in the world
- Is the second illness lighter or more severe than the previous one? There is currently no clear answer to this question
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One year has passed since the first reported case of SARS-CoV-2 infection, but there are still many unknowns related to the epidemiology of this virus. One of the key questions is how long an acquired immune response lasts and how long is it able to prevent another infection. For seasonal coronaviruses, immunity is short-lived, with re-infections occurring after an average of 12 months.
A study carried out in Kenya showed that in 4-21 percent. People infected with endemic coronaviruses (HCoV-229E, NCoV-NL63, and HCoV-OC43) have had two or more episodes of infection with the same virus variant over a period of approximately six months. The described cases of COVID-19 recurrence show that resistance to SARS-CoV-2 may also decline relatively quickly. This poses a risk to already healed patients and raises doubts as to whether vaccines can provide long-term protection.
So far, the phenomenon of reinfection with SARS-CoV-2 virus does not appear to be widespread. So far, several hundred probable cases have been reported, with almost 70 million infections worldwide. The low number of confirmed reinfections may be due to the fact that their identification is difficult. Researchers cannot simply rely on patients’ reports of symptoms or mere tests for the presence of the virus. PCR enables the detection of SARS-CoV-2 viral RNA in the upper respiratory tract after infection for up to 83 days. It is therefore necessary to confirm the alleged cases of reinfection by sequencing the genome of viruses from the first and second diseases and compare whether they are different virus variants. If serum is available, it would also be wise to consider serological testing to determine the immune response to initial infection and suspected reinfection.
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In conclusion, reinfection cannot be confirmed if clinical samples from the first episode are not available, which is a common situation. As a result, the number of genetically confirmed repeat infections is an order of magnitude lower than the number of suspected reinfections.
A recent study in Qatar identified 243 potential reinfections based on medical history, but only 12 patients had sufficient data on the virus genome. Two of these cases had identical viral genomes on the first and second positive tests, suggesting persistent infection, and six others did not have enough genetic changes to make a firm conclusion about reinfection. Only four had genetic material to confirm reinfection. The Netherlands has 50 such cases, Brazil 95, Sweden 150, Mexico 285.
The first genetically confirmed case of reinfection was in a 33-year-old man who was treated in a Hong Kong hospital in March for mild COVID-19. On August 15, he tested positive again at the airport after returning from a trip from Spain. The second infection was asymptomatic, laboratory tests revealed only a slightly elevated concentration of C-reactive protein. Similar cases of asymptomatic reinfection discovered during routine testing have been reported in India. A 25-year-old man and a 28-year-old woman, health professionals, were re-diagnosed with infections approximately 3 months after the first infection.
However, not all reinfections observed so far are milder. The 51-year-old Belgian woman developed headaches, cough and fatigue with both the first and the second infections. Two cases were also reported where reinfection was more severe. This was the case with a 25-year-old man from the United States and a 46-year-old man from Ecuador. All of these people were under the age of 60 and had no immunodeficiency from other diseases. To date, at least 24 other reinfections have been officially confirmed. They may become more common in the next few months if the early cases begin to lose immunity.
Secondary infection may result from insufficient immune stimulation on first contact with the virus or a weakening of the antibody response over time. Understanding the pattern of immune memory function is important in assessing the chance of recurring infections. So far, neutralizing antibodies, memory B cells, CD4 + T cells, and CD8 + T cells have been found to exhibit different kinetics in SARS-CoV-2 infections, but all appear to be relatively stable for at least 6 months. This means that immunity may weaken over time – as is the case with other types of coronavirus, but should last a minimum of six months.
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In addition to the patient’s immune system response itself, SARS-CoV-2 virus evolution could also play a potential role in reinfection. In a paper published in September, 80 natural variants of the S protein were analyzed for their infectivity and sensitivity to antibodies or convalescent serum samples. Fortunately, the strain with the D614G mutation in the viral S protein, the major variant currently circulating around the world, appears to be remain susceptible to neutralization by both convalescent serum samples and a panel of monoclonal antibodies specific for the S.
However, a recent article published by the Swedish Medical Center in Seattle suggests that a variant of the virus with reduced susceptibility exists. The team describes a person who became infected in March and reinfected 4 months later. The second virus had a mutation that causes a slight change in the virus’s output protein, which helps it enter human cells. Although the symptoms were milder the second time around, experiments have shown that antibodies caused by the first virus do not work well against the second.
Such reports show that being infected with SARS-CoV-2 does not guarantee permanent immunity. Until effective treatments and prevention of COVID-19 have been found, maintaining social distancing and wearing masks are still the best means of personal protection.
Author: Magda Mazurek / Medexpress
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