Places like Brazil, where the transmission of the cause of Covid-19 continues to occur on a large scale, tend to transform into factories of new forms of the virus, making it easier for more transmissible strains to emerge. According to experts, the only way to prevent the further emergence of potentially more dangerous versions of Sars-CoV-2 is to reduce the spread of the virus in the population.
“Viruses are designed to mutate [modificações aleatórias no material genético]”Explains Flávio da Fonseca, researcher at UFMG (Federal University of Minas Gerais) and President of the Brazilian Society of Virology. “Every time one of them infects a person, they create dozens, hundreds of mutations, most of which are harmful and don’t even go forward – it just ceases to exist right there.”
Although viral invaders exercise some quality control over their genetic material and sometimes hijack human cellular mechanisms to do so, it is a naturally “loose” control that allows mutations to occur frequently as they reproduce.
The point is that while almost all of these modifications are useless or neutral, some of them are capable of improving the spread of viruses. For example, they can increase their replication rate (roughly how quickly new viral copies are made) or strengthen their connections to receptors, the “ports” through which they enter cells.
What determines which of these variants will predominate in the virus population in the future is natural selection – that is, the viruses that reproduce more efficiently are the ones that leave more offspring than the others. It turns out that in a situation where many people are infected – that is, many new virus mutations appear in thousands or millions of patients – much more of the raw material for natural selection “works”. Thus, the likelihood of mutations occurring with a greater ability to spread increases sharply.
“It’s an almost mathematical and very intuitive process,” says virologist Maurício Lacerda Nogueira, professor at the Medical Faculty of São José do Rio Preto. “We see this clearly in the dengue and yellow fever strains, two viruses from the same family that are very close to each other. The diversity of dengue viruses widely distributed among the population is much greater than that of yellow fever, which is much less circulating. The same thing happened with strains of HIV, the diversity of which exploded in the Caribbean before the 1980s and then in the United States in the 1980s when the virus began to circulate in large numbers in the population. “
For Fonseca, the process happens in such a way that it is necessary to reverse the logic that is sometimes used to explain the recent public health collapse in Manaus caused by Covid-19. “This whole drama was ascribed to the appearance of the so-called variant P.1. In fact, it’s the opposite: it was the lack of control, failure to keep distance and other measures that allowed the variant to appear, ”he muses.
Virologist Fernando Spilki, professor at Feevale University (RS) and coordinator of the Corona-ômica network of the MCTI (Ministry of Science, Technology and Innovation), says that the current data suggests that the P.1 variant is already Brazilians reached other states in December. The other common variant is known as P.2. “The virus continues to evolve: the initial P.2 variants didn’t have all of the mutations we find today, and we’re also starting to show additional mutations in P.1,” he says.
What should happen when transmission rates are more controlled, especially thanks to vaccination?
“The usual situation is that after a long time the virus reaches a stage of better genome preservation with fewer variations, as we see, for example, as the years pass after new strains of influenza have been introduced [vírus da gripe]Says Spilki. The trend is therefore that the transmission rate stabilizes and the virus becomes endemic (neither disappearing nor increasing sharply in cases of illness).