The BA.2.75 subvariant of the coronavirus has worried specialists and health institutions due to its high transmission capacity. Registered for the first time in May in India, it has a set of mutations never seen before – which could be an explanation for its spread.
The strain is currently being monitored by the WHO (World Health Organization). In addition to India, it has already been registered in ten countries. In Brazil, the subvariant has not yet been identified through sequencing.
The virus is part of the lineage of the ômicron, which remains the dominant variant of concern in the world. BA.2.75 is an offshoot of the BA.2, a variant of the omicron that had its first cases in Brazil in February this year.
“In India, we have a more expressive scenario [para a BA.2.75]. What caught our attention is that it quickly spread to other countries,” says Fernando Spilki, virologist and coordinator of the Corona-Omics BR-MCTI Network, a laboratory project that sequences the genomes of Sars-CoV-2 samples in Brazil.
The concern is also due to the spread of the strain compared to other variants. According to Denise Garrett, epidemiologist and vice president of the Sabin Institute (USA), “apparently [a BA.2.75] is spreading faster than other variants circulating”.
Spilki also draws attention to this point. He says that BA.2.75 managed to spread considerably in environments that already had a large presence of other highly transmissible subvariants, such as BA.4 and BA.5.
BA.2.75 accumulates a series of mutations that had not yet been observed. According to the WHO, in addition to those already registered in BA.2, the subvariant has eight new mutations in the spike protein, which facilitates the entry of the virus into cells. In addition to these, BA.2.75 also has five other mutations.
It is through the spike protein that the coronavirus invades human cells. Therefore, the more mutations a variant accumulates in this protein, the chances of greater transmission increase.
“What is known so far is that this set of mutations facilitates transmission”, says Raquel Stucchi, an infectious disease specialist and professor at Unicamp (State University of Campinas).
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The indications of greater transmission of BA.2.75 raise an alert for the impact it may have on the Covid-19 pandemic. However, it is still not possible to say with certainty that this is the subvariant with the highest transmissibility ever recorded.
“It’s still too early to make statements about the transmissibility of the strain,” says Garrett.
WHO Chief Scientist Soumya Swaminathan explained in a July 5 organization video that there are still very few sequencing of the subvariant available for analysis. Thus, it is not possible to conclude the degree of transmission and the severity of the clinical conditions of BA.2.75.
Another aspect is that the behavior of the virus can vary across countries, says Spilki. He exemplifies the case of the delta variant in Latin America: although it has had a huge impact in some parts of the world, such as the United States, this strain has not played such a major role in Latin countries compared to the gamma variant.
At the moment, he believes that the trend is for the continued growth of the subvariant BA.5 to the detriment of BA.2.75. “But we know that this situation can change quickly,” he points out.
WHO Director-General Tedros Adhanom Ghebreyesus also indicated at a conference on the 6th that, in the American and European continents, subvariants BA.4 and BA.5 are causing new waves of cases. Regarding BA.2.75, Ghebreyesus indicated that she is being followed up.
severe cases
In addition to transmission, another intriguing aspect is whether BA.2.75 can cause more severe cases of Covid-19.
According to Garrett, the milder cases of the disease occur mainly because most of the population has already developed some type of immunity – either from the vaccine or from previous infections with Sars-CoV-2.
“The greater the immune escape of the variant, the more likely it is to cause more severe conditions,” says Garrett.
The epidemiologist also explains that, in the case of BA.4 and BA.5, the vaccines proved to be effective against hospitalizations and serious conditions. “As for BA.2.75, we still don’t have enough information,” she adds.
Infectologist Stucchi also explains that the issue of the development of more severe conditions with BA.2.75 remains open. However, she points out that vaccines, by applying additional doses, continue to be effective in preventing complications, even in the case of subvariants.
Therefore, the infectologist says that the new mutations of Sars-CoV-2 “represent a threat to Brazil” when considering the low adherence of the population to vaccination with booster doses.
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