At the beginning of the pandemic, many were convinced that COVID-19 was a once-in-a-lifetime disease. Shot, got antibodies – rest. However, as more and more data on re-infections began to emerge, optimism gave way to pessimism. Now there is almost no doubt that the coronavirus has stayed with us forever and nothing guarantees eternal protection against it: neither disease nor vaccination.
The authors of a new study, published in The Lancet, made complex calculations based on a study of the genomes of various coronaviruses, and concluded that, on average, everyone on the planet will get SARS-CoV-2 every 16 months. That is, twice as often as seasonal coronaviruses.
The duration of immunity to the SARS-CoV-2 virus is still a debated issue. Initially, scientists gave very different assessments on this matter. Someone assumed that immunity could last for a year, someone – that up to five years. Optimists even put forward a version of 11-year immunity, based on the experience of the last outbreak of the first SARS-CoV in 2004. However, reality has refuted the most daring assumptions: cases have become known when people fell ill again after a few months.
The authors of the new publication in The Lancet tried to estimate how often we will get sick with COVID-19 as part of the strategy “living with the virus.” The researchers analyzed the data on the resistance of immunity in evolutionarily close six SARS-CoV-2 related coronaviruses, which infect humans, by comparative analysis of their genomic sequences. They also examined various medical studies showing that immunity to coronaviruses can last from 128 days to 28 years after infection.
It turned out that the SARS-CoV and SARS-CoV-2 viruses are very closely related, MERS-CoV is also their “close” relative, but the four seasonal coronaviruses that cause mild colds in humans are much further from this group. The researchers assessed the profiles of the typical decline in antibody levels and the likelihood of reinfection over time in a pandemic. It turned out that the most persistent immunity is given by seasonal cold-related coronaviruses: in humans, protection against re-infection with them ranges from 15 months to 12 years. But for SARS-CoV-2, the calculations showed the possibility of re-infection in the period from 3 months to 63 months after the peak of antibodies, with a median of 16 months. This is half the rate of the seasonal cold coronaviruses circulating among humans.
The time to reinfection estimated in this work is consistent with the small number of confirmed reinfection cases. However, scientists warn that as the COVID-19 pandemic continues, re-infections will become more frequent, and people will have to make a lot of efforts to contain the transmission of the virus.
Scientists note that understanding the timing of reinfection is important for public health decision-making, including imposing travel restrictions, opening and closing economic sectors in response to predictive patterns of the epidemic. So, they note that people who have recovered from COVID-19 can only be viewed as temporarily immune to re-infection. “Our assessment strongly refutes the claim that herd immunity from natural infection can resolve the epidemic, or that the long-term risks of morbidity and mortality can be reduced without vaccination. By relying on herd immunity alone, we endanger millions of lives with high rates of reinfection, morbidity and mortality. In areas with low vaccination rates, our analysis confirms the need for continued social distancing practices, proper ventilation of the premises and the wearing of masks. People’s overconfidence in long-term immunity following natural infection with SARS-CoV-2 contributes to vaccine hesitation, possibly due to false equivalence with long-term immunity after natural recovery from viruses that cause diseases such as measles, mumps and rubella. But numerous respiratory viruses, including coronaviruses, can overcome the immunity created by previous infections through the evolution of new variants. A little over a year after the COVID-19 pandemic, new variants of SARS-CoV-2 began to appear, which can vary in the severity of the infection and cause various reactions of the immune system, as well as interfere with the resistance of the immune system, ”the authors of the work note. In their opinion, the inability to manage the pandemic will doom us to an endless cycle of chasing the pathogen that changes its shape.
In addition, the researchers emphasize that their assessment is important for predicting the development of a pandemic as a whole, although in “peacetime” the risk of reinfection for each individual is extremely low. “However, during a pandemic, when hundreds of thousands of people are infected, such rare events with a measurable frequency are very likely and could have significant consequences for public health,” the scientists write in The Lancet.
Meanwhile, some experts are reluctant to agree that re-infections will rise as the pandemic progresses. “I, for one, have not seen any studies showing this trend. Re-ill as it was a year ago 1–5%, and now the same, ”- said data analyst Maxim Bobrov.
“The authors of the work investigated only the possibilities of humoral immunity, that is, the presence of antibodies. There was evidence that cellular immunity to the new coronavirus could persist for more than five years. However, the mere presence of antibodies or memory cells and even their number, as practice shows, does not indicate the level of protection against re-infection. At the same time, the neutralizing ability of antibodies in those who have been ill is very high, therefore, even a concentration below the reference values does not necessarily mean a lack of protection against infection, “molecular biologist Daniil Vetrov told MK.
Another issue that worries scientists, doctors, and people is the severity of the disease in case of reinfection. Alas, it is still impossible to predict it. Is it possible that people will get sick more and more every time? Should SARS-CoV-2 evolve to eventually kill us all?
Doctor of Biological Sciences, Skoltech Professor Konstantin Severinov says that it is impossible to predict the evolution of the virus, but the experience of vaccinated and recovered patients shows that they get sick again much less often and get sick more easily: next time from a heavy current. Of course, stories about people who were sick more severely the second time are passed from mouth to mouth, but more often than not they are not confirmed. These are just popular myths and urban legends. “
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