In one month, the sublines BA.4 and BA.5 of the omicron started to represent 44% of the positive samples of Covid-19 in Brazil, according to a report by the All for Health Institute (ITpS). The rate before was just 10.4%. Therefore, points out the ITpS, there was an increase in cases and hospitalizations.
The institute estimates that there will be a peak transmission of BA.4 and BA.5 this week and, throughout June and July, a drop in positivity in tests and, consequently, in cases. After arriving in the country in May, the two strains have already been identified in 198 municipalities in 12 states and in the Federal District.
According to the World Health Organization (WHO), BA.4 and BA.5 carry a mutation that seems to be related to greater transmissibility and immune escape – either from previous infections or from the vaccine. Evidence from several countries, however, indicates that they did not increase the severity of cases. The greater transmissibility is explained by the increased ability of the virus to bind to the human cell. This allows even a lower viral load to cause infection.
The moving average of infections has increased by 114.8% in the last two weeks, according to data from the media consortium. On Thursday, the number stood at 37,191, which shows a return to the levels seen at the end of March, but far from the peak of the “original” Ômicron, BA.1. The upsurge may be underreported because of self-tests and problems in reporting by states.
The advance of cases and sublines occurs at a time of stagnation in vaccination rates and cold temperatures, when people tend to stay in closed spaces, closer together and with the circulation of other worrying respiratory viruses. To avoid a possible increase in hospitalizations and mortality, experts indicate the need to encourage immunization, especially in booster and pediatric doses, and the return of mandatory masks in closed places.
Between March 1st and June 4th, ITpS analyzed more than 123,800 RT PCR tests performed by private laboratories. About 90% of the samples are from the Southeast and Midwest. The current positivity rate is 38.9%.
Virologist and researcher at ITpS, Anderson Brito highlights that the data do not come from sequencing, but from genotyping. They analyze the detection of the S gene of the virus, which makes it possible to say what the likely underline of Ômicron is.
BA.1 arrived in the country in December. It replaced the Delta variant and was dominant between January and February. Starting in March, BA.2 slowly gained ground and reached its apex in mid-May, when BA.4 and BA.5 came on the scene. As Brito explains, BA.4 and BA.5 have an evolutionary advantage over BA.2. Both have a greater ability to transmit and also escape the immune response. “Until the middle of last month (with BA.2), we were basically experiencing a wave of small dimensions, because the number of cases has not gone up that much.”
The wave of cases driven by underlining, he says, “serves as a warning”. However, Brito highlights that there is a “positive point”. “South Africa was the first country that faced all these sub-variants. And the recent wave (driven by BA.4 and BA.5), which ended a few days ago, was the one with the shortest duration and the one that had the least impact on public health,” he says, highlighting the merits of vaccination. “This shows us a less unfavorable scenario compared to waves that we have already faced.”
But the risk is not non-existent. “These two variants have predominated in the last two months in Europe. And they were responsible for a new increase in cases and also in hospitalizations there”, says infectious disease specialist Raquel Stucchi, from the Brazilian Society of Infectious Diseases. She highlights that the vaccinal leakage of sublines is related to infection and mild cases. Immunizers continue to offer robust protection against severe conditions.
But for that, it is necessary to have an adequate level of antibodies, which raises the alert for the need to advance in the application of reinforcements. “Within four or five months, especially in the immunocompromised population and in those over 50 years of age, there has already been a drop in antibodies.”
People who have not yet been immunized or who have not completed the dosing schedule are also more vulnerable in this wave of sublines. “We know that deaths and ICU admissions occur 20 times more often in unvaccinated or incompletely vaccinated individuals”, reinforces Marcelo Otsuka, vice president of the Department of Infectious Diseases at the São Paulo Pediatric Society (SPSP).