The already known coronaviruses, which cause harmless colds, infect humans at regular intervals. It appears that SARS-CoV-2 will behave in the same way. After all, scientists worldwide report new infections of covid-19 confirmed by laboratory tests on an almost daily basis.
One of the mysteries of the new coronavirus is how long the immune system protects us after an infection. Since SARS-CoV-2 has only recently entered humans, research on covid immunity is in its infancy. That is why scientists are happy to go back to what they already know and what most closely resembles SARS-CoV-2, such as the four long-known coronaviruses (HCoV-NL63, HCoV-229E, HCoV-OC43 and HCoV-HKU1).
One of the mysteries of the new coronavirus is how long the immune system protects us after an infection. Since SARS-CoV-2 has only recently been in humans, research on covid immunity is in its infancy. That is why scientists are happy to go back to what they already know and what most closely resembles SARS-CoV-2, such as the four long-known coronaviruses (HCoV-NL63, HCoV-229E, HCoV-OC43 and HCoV-HKU1). (not peer-reviewed) of the Dutch institution Amsterdam UMC shows that it often takes ‘alarmingly short’ before people become infected with a corona cold a second time. ‘It is likely that exactly the same applies to the new coronavirus SARS-CoV-2’, the scientists write. “ Precisely because the viruses differ greatly and we find the same result for all viruses, we think this is a common property of all coronaviruses, ” says researcher Arthur Edridge. Earlier, American virologist who advises the White House on corona, Anthony Fauci , already record that SARS-CoV-2 will behave like the other coronaviruses. “If you look at the history of the coronaviruses, it turns out that protective immunity varies from three to six months to almost always less than a year,” said the virologist. Although SARS-CoV-2 sometimes dares to deviate from expectations, it seems that immunity to covid-19 will also fade over time and may prevent reinfection. In a few years, SARS-CoV-2 may even become an annual seasonal cold like the others. Research into how the immune system responds to SARS-CoV-2 has focused mainly on antibodies in recent months. These are proteins that attach to the surface of the pathogen and prevent it from infecting cells in the body. It has already been shown that the antibodies disappear from the blood after a short time. In fact, people with mild symptoms don’t produce antibodies at all. Still, that’s no reason to panic. Antibodies are just one of the weapons of the immensely complex human immune system. Another component are immune cells, such as T cells, that create memories for future infections. These memory cells can quickly identify and destroy a second infection that antibodies may be out of control. B cells are in turn able to produce brand new antibodies. Several studies show that both T and B cells work perfectly against SARS-CoV-2 and offer some form of protection. In addition, T cells persist for a long time in people with mild symptoms. That is the group that makes up the majority of this pandemic. With age, the number of T cells that can be used against a particular virus decreases, which could be a possible explanation for why older people are more affected, while in the first wave ‘reinfections’ were explained by a reactivation of the same virus in cured patients and on the other hand false positive tests, effective reinfections (an infection with a slightly modified form of SARS-CoV-2) are now also coming to light. For the time being, it only concerns a few cases. This means that it is either a rare phenomenon or that reinfections are more difficult to detect because genome analyzes of positive cases are not very common. So we know that reinfestations are possible, but not how often they occur. The cases described show that the disease course of a recontamination is not unambiguous. A 33-year-old patient in Hong Kong had no symptoms (peer-reviewed) the second time, as did two Indian health professionals (not peer-reviewed). A Belgian patient showed only mild symptoms upon reinfection (peer reviewed). This is good news, as it indicates that the immune system is remembering the first infection and can act appropriately. But a 25-year-old patient in Nevada had more severe symptoms with a second infection and even had to be admitted to hospital for a while (not peer-reviewed). This could mean that the severity of the disease varies not only from person to person, but from infection to infection in the same person, depending on the dose of the virus, possible differences between variants of the virus or a change in general health. the patient himself. The immune system can also overreact with reinfection, as we saw in patients in the first wave. In rare cases, antibodies to SARS-CoV-2 may be able to help the virus with a second infection. This phenomenon of ‘antibody-dependent enhancement’ has also been previously identified in the attempt to develop vaccines against SARS-CoV-1 and MERS, the cousins of the novel coronavirus. And what about the corona vaccines? Will we have to get an injection every three months or can vaccines give us the protection that our natural defenses cannot? The easiest situation for vaccine makers is when an infectious disease generates lifelong immunity, such as measles and rubella. Respiratory viruses usually do not do this, so that a corona vaccine may not be able to prevent a second infection, but it will moderate the disease course, which is also a nice bonus in this corona pandemic. A possible bright spot is that the immunity elicited through a vaccine may be more potent and more protective than the immunity from a natural infection. For example, natural immunity against the papilloma virus, which causes cervical cancer, is rather weak. A high concentration of the surface protein of the virus in the vaccine produces stronger antibodies and provides better protection. In addition, many viruses try to switch off the immune system during an infection, while vaccines obviously do not have that property. Vaccines, on the other hand, contain additives that improve their effect. A gift for vaccine builders is that coronaviruses are known to mutate very slowly. They are among the slowest mutating RNA viruses known in contrast to HIV or influenza viruses that mutate every year. Despite the fact that SARS-CoV-2 has already undergone thousands of mutations since its outbreak in Wuhan, China, these have not substantially changed the course of the covid-19 disease for the time being.
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