One day, pandemic will end. Scientists don’t know how that ending will play out, but a new model offers a teaser: the deadly SARS-CoV-2 may not entirely disappear, but instead become a common circulating cold virus that causes only a few mild colds.
This model, published on January 12 in the magazine Science, is based on analyzes of other coronavirus, most of which cause only mild symptoms in humans. There are six known coronaviruses that infect humans; four are coronaviruses “endemic” or that circulate regularly among human populations and cause the common cold.
The other two coronaviruses – those that cause severe acute respiratory syndrome (SARS) and Middle Eastern respiratory syndrome (MERS) – are more deadly, although the former was eliminated years ago and the latter was largely contained.
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To create their model, a group of researchers analyzed previously published data on the four lightest coronaviruses and found that “the immunity that blocks the infection decreases quickly, but the immunity that reduces the disease is long-lived,” wrote the authors in the study. In other words, people can get infected repeatedly, but they rarely develop serious illnesses, said lead author Jennie Lavine, a postdoctoral fellow at Emory University in Atlanta, said in a statement.
Almost everyone catches one of these endemic coronaviruses during childhood; and these initial infections confer partial immunity to adults who are reinfected. “Reinfection is possible within a year, but even if it does, the symptoms are mild and the virus is cleared from the body more quickly,” said Lavine.
But there is no similar long-term data on the duration of immunity for the new coronavirus SARS-CoV-2 that causes COVID-19. It is not clear how long immunity, whether from vaccines or natural infection, to SARS-CoV-2 will last in people; it is also not known to what extent vaccines and natural infections can contain transmission or reduce the severity of the disease.
Some people have already been reinfected with SARS-CoV-2, Live Science previously reported. But these cases are rare and most of these people had the mildest disease the second time, according to the study.
The model assumes that immunity to SARS-CoV-2 will work similarly to these other endemic coronaviruses, Lavine said. And one of the main conclusions of the model is that, for existing coronaviruses, the severity of the infection during the endemic phase is directly linked to the severity of the disease when it infects children. Unlike the new coronavirus, almost nobody finds them for the first time as an adult. But “we don’t really know what it would be like if someone caught one of the other coronaviruses for the first time as an adult, rather than as a child,” she said. It is possible that, if they did, they would experience a more serious illness.
The model predicts that if SARS-CoV-2 becomes endemic and future generations are exposed mainly during childhood, the virus “may not be more virulent than the common cold,” wrote the authors. Once endemic, the death rate from infection with the virus, or the number of people who die compared to those who are infected, will fall below the seasonal flu, wrote the authors.
This is because children are generally less severely affected by COVID-19 infections and mortality is usually low in children, so this underlying severity must predict the severity of SARS-CoV-2 in its endemic phase. But if SARS-CoV-2 severely impacted children, as is the case with the virus that causes MERS, then, even during the endemic phase, a relatively high number of people could die, the authors predicted.
If this model is true, exactly how the world will reach the endemic stage still depends on us: The faster spread of the virus will result in a faster transition as people gain herd immunity, but will result in more deaths. Vaccines are a safer way to achieve this immunity and, once widely available, will also accelerate the transition to a possible endemic phase – a phase where the coronavirus can be attacked with a box of tissues, rather than fans. and lockdowns.
Originally published on Live Science.