SARS-Cov-2 probably came from the combination of two coronaviruses that infected the same animal. What if this process repeats itself in humans and leads to a new pandemic?
Many fears have emerged in recent months about a possible SARS-Cov-2 mutation that would have made it more virulent or infectious. But it is another threat that concerns some researchers today: that of a recombination of the virus with another common coronavirus, which would lead to a new hybrid and a new pandemic.
Several elements support this hypothesis. First, coronaviruses tend to recombine easily as it is one of their main modes of evolution. Compared to other RNA viruses, which tend to evolve by mutation, coronaviruses are quite stable because they have enzymes that superficially “verify” that the RNA copy is free of errors. As a result, few SARS-Cov-2 mutants are known to date, and even then they are minor mutations.
Recombination, the preferred evolutionary mode of coronaviruses
To evolve and deceive the resistance of the immune system, coronaviruses have another tactic. Their replication enzymes often jump from one part of the RNA matrix to another, allowing them to rapidly remix their genome and “steal” material from other related coronaviruses. One study, by researcher Huiguang Yi of Shenzhen University of Science and Technology (China), studied 84 genomes of SARS-Cov-2 and showed that some strains could only be formed by recombination with another strain.
Possible co-infection with other viruses
However, a second condition is necessary for recombination with another coronavirus to occur. The same person must be infected with both coronaviruses simultaneously, and both coronaviruses must be present in the same cell which is very rare, but not impossible.
Especially because the coronavirus is perfectly capable of coexisting with other viruses, and several cases of co-infection with the flu virus, respiratory syncytial virus (RSV), or other common cold viruses have been documented. The latter is of great concern because they are coronaviruses close to SARS-Cov-2 and therefore more likely to recombine easily with it. It is also possible that SARS-Cov-2 could be found in a person infected with MERS-CoV, another coronavirus that still circulates occasionally. This hybrid would then create a completely new disease.
The third element that supports the recombination thesis is that SARS-Cov-2 may itself be a mixture of two other coronaviruses. One hypothesis is that it is derived from a pangolin virus and a bat coronavirus that found themselves by chance in the same host. However, in humans, this cohabitation is far from obvious.
Very often, the virus that arises from such recombinations is not very viable. During the replication cycle, the proteins of different viruses interact with each other and are often incompatible. Today, there are no examples of recombination among the four cold coronaviruses that have been circulating for several years. For the same reason, recombination with a very different virus such as the flu is even more unlikely.
A “universal” vaccine against all coronaviruses?
So, is there any reason for concern? Would such recombination threaten a future vaccine? It all depends on what part of the virus is involved. If it is a surface protein of the virus, the one used by the immune system to identify the pathogen, then the vaccine will actually be less effective. But if it’s an internal part of the virus, like polymerase [used for replication], then it shouldn’t matter. Ideally, a “universal” vaccine targeting this polymerase, for example, would be effective against all strains of coronavirus at the same time.
Finally, even if the virus were able to recombine, there is no reason to believe that this new hybrid would be more aggressive. On the contrary, it could be benign to humans, like many other coronaviruses.