Researchers have set up a likely scenario for the evolution of Covid-19: As reinfections occur, the immune system adapts and causes less severe forms, as in the case of the common cold.
“The virus is with us forever,” WHO warned last November, leaving little hope that the situation would normalize in the near future. Although the number of deaths caused by the coronavirus has surpassed 2 million and the number of cases is approaching the 100 million mark, a new study in the journal Science also suggests that the covid epidemic may never end. But once enough adults are immunized (either with the vaccine or the disease), it will become as mild as the common cold and will circulate in relatively small amounts. “How long it takes to reach that stage depends on how quickly that herd immunity is achieved. The sooner most people are infected or vaccinated, the sooner we will reach this endemic stage,” says Jennie Lavine, a postdoctoral fellow at Emory University in Atlanta and lead author of the study.
The researchers compared SARS-Cov-2 to the six other coronaviruses that infect humans (the four cold viruses, SARS and MERS). According to the study, the new coronavirus behaves like the viruses that cause the common cold. The common cold usually first affects children between the ages of 3 and 5, when the illness is less severe than in adults. After that, the infections are repeated regularly until the immune system is strong enough that the infection causes only mild symptoms. In other words, the virus continues to circulate but no longer causes death. It is very similar to the vaccine: it does not prevent transmission, but it helps limit the number of severe cases.
The vaccine is less effective than natural infection
However, there are exceptions to this relatively optimistic scenario. MERS, for example, does not follow this model because it is highly lethal to children. In this case, early vaccination, as with measles, would be essential. Furthermore, what would happen if the virus mutated? It wouldn’t make much difference, according to Jennie Lavine and her colleagues. “Frequent reinfection with different strains builds immunity to other coronaviruses,” they write. However, this may be less true with vaccine immunity because the vaccine has fewer epitopes.
Unfortunately, by the time the virus reaches this endemic phase, which could last “several decades,” Covid-19 still has time to do a lot of damage. The vaccine is our only hope of stopping it sooner.