If we create opportunities for the virus to circulate, it will take them.
Uma nova subvariante do coronavírus, batizada de Kraken, avança pelo mundo com uma capacidade incomum de escapar das defesas imunológicas construídas por vacinas e infecções anteriores. Em poucos dias, o XBB.1.5 tornou-se a cepa dominante nos Estados Unidos e já foi detectado em mais de 25 países, lembrando-nos de que a pandemia ainda escreve seus capítulos. O Brasil, como tantas outras nações, não está imune a essa chegada — e a questão que se coloca não é se o vírus virá, mas o que faremos quando ele chegar.
- O XBB.1.5 dobrou as internações em UTIs nos Estados Unidos em poucas semanas, combinando alta transmissibilidade com uma capacidade perturbadora de driblar anticorpos de vacinas e infecções anteriores.
- A variante corrigiu uma falha genética de sua cepa-mãe asiática, tornando-se mais eficiente para infectar células humanas — uma evolução viral que preocupa especialistas pelo mundo.
- A abertura repentina da China após anos de política de 'COVID zero' lançou centenas de milhões de pessoas sem imunidade prévia ao vírus, criando um caldeirão global de circulação viral.
- Virologistas brasileiros são unânimes: a chegada do Kraken ao Brasil é praticamente inevitável, e o país entra nesse momento sem medidas de contenção na fronteira e com baixas taxas de reforço vacinal entre adultos jovens.
- A defesa possível existe — vacinas bivalentes, máscaras em ambientes fechados e, sobretudo, a cultura de testar e isolar — mas depende de uma adesão coletiva que ainda não está garantida.
A Organização Mundial da Saúde emitiu um alerta no início de janeiro sobre o XBB.1.5, subvariante do Omicron apelidada de Kraken — referência ao monstro marinho da mitologia — que avança rapidamente pelos Estados Unidos e pela Europa. Em apenas uma semana, sua participação nos casos americanos saltou de 20% para 40%, chegando a 75% em Nova York. A principal ameaça não é necessariamente uma doença mais grave, mas a capacidade da variante de escapar dos anticorpos gerados por vacinas ou infecções anteriores, combinada com uma transmissibilidade elevada.
O XBB.1.5 descende de uma cepa que surgiu na Ásia, mas que tinha uma limitação: perdia eficiência ao se ligar às células humanas. Uma nova mutação corrigiu esse problema, resultando em um vírus que se espalha com facilidade e contorna as defesas imunológicas simultaneamente. Nos hospitais americanos, as internações em UTIs dobraram desde a chegada do Kraken, embora o número total de casos ainda seja muito inferior ao pico do Omicron original, há um ano.
O cenário global é agravado pela China, que abandonou abruptamente sua política de 'COVID zero', desencadeando uma explosão de infecções em uma população com pouca exposição prévia ao vírus e cobertura de reforço vacinal insuficiente. A subnotificação torna difícil avaliar a real dimensão do surto no país.
No Brasil, virologistas ouvidos pela reportagem são categóricos: a chegada do XBB.1.5 é quase certa. Fernando Spilki, da Universidade Feevale, lembra que o XBB já circulou no país. Flávio Guimarães da Fonseca, da Sociedade Brasileira de Virologia, diz que a questão não é 'se', mas 'quando'. Isaac Schrarstzhaupt aponta que nenhuma medida de contenção foi adotada nas fronteiras. O risco de uma nova onda existe, especialmente considerando o padrão histórico de surtos após as festas de fim de ano e o retorno das atividades em fevereiro e março.
A proteção disponível é real, mas exige compromisso coletivo. As vacinas bivalentes oferecem maior proteção contra as variantes Omicron em circulação. Máscaras em ambientes fechados e lotados continuam sendo ferramentas válidas. E, talvez mais urgente, especialistas pedem uma mudança cultural: testar, saber quando se está infectado e isolar-se. Como resume Spilki, vacinar e tomar precauções não basta — sem o teste, o vírus circula invisível, carregado por quem nem sabe que o porta.
The World Health Organization issued a warning on January 4th about a new coronavirus subvariant spreading rapidly across the United States and Europe. Called XBB.1.5—nicknamed Kraken after the mythical sea monster—this latest mutation of Omicron has become the dominant strain in American infections, accounting for roughly 40 percent of cases nationwide, up from 20 percent just a week earlier. In New York City and surrounding regions, the variant is responsible for three-quarters of all infections. The U.S. Centers for Disease Control and Prevention cautioned that XBB.1.5 "may be more transmissible than other variants," though scientists remain uncertain whether it causes more severe illness.
The variant's particular danger lies in its ability to evade immune protection. American experts have found that XBB.1.5 is harder for antibodies to neutralize, whether those antibodies come from vaccination or previous infection. This immune escape capacity, combined with its transmissibility, earned it the Kraken designation. The parent strain, XBB, almost certainly emerged in Asia, where it triggered a surge of cases during autumn. That original version had a weakness—it lost some efficiency in binding to human cells. XBB.1.5 corrected this flaw through a new mutation, restoring the virus's ability to infect cells with high efficiency. The result is a variant that spreads more easily and slips past existing defenses simultaneously.
U.S. hospitals have recorded rising admissions over the past month, with intensive care unit admissions doubling since Kraken's arrival and deaths climbing. Yet the picture is complicated. The northwestern United States, where XBB.1.5 prevalence is highest, has not seen hospitalizations rise disproportionately compared to other regions. Experts attribute some of the spread to social factors—holiday gatherings and winter behavior patterns that push people indoors into close quarters. The overall case surge, however, remains significantly smaller than a year ago, when the original Omicron wave generated nearly 25 million confirmed diagnoses weekly globally, roughly seven times current levels. Testing has declined substantially as cases have become milder and more people rely on home tests rather than official reporting.
The emergence of Kraken coincides with China's abrupt abandonment of its "zero-COVID" policy, triggering an explosion of infections across the country. Chinese authorities report that variants BA.5.2 and BF.7 dominate there, accounting for more than 80 percent of cases. The surge reflects the Chinese population's limited prior exposure to the virus, gaps in booster vaccination coverage, and reliance on vaccines using traditional technology rather than the mRNA approach used by Pfizer and Moderna. Substantial underreporting of cases in China makes it difficult to gauge the true pace of spread.
Brazil faces near-certain arrival of XBB.1.5, according to virologists interviewed about the threat. Fernando Spilki, a virologist at Feevale University, stated it is "almost impossible" the subvariant will not reach Brazil, noting that XBB circulation has already occurred there. Flávio Guimarães da Fonseca, president of the Brazilian Society of Virology and a professor at the Federal University of Minas Gerais, framed the question not as whether the variant will arrive but when. Isaac Schrarstzhaupt, coordinator of the COVID-19 Analysis Network, observed that Brazil has implemented no measures to prevent the variant's entry. The potential for a new wave exists, though experts cannot predict its scale with confidence. Historically, Brazil experiences significant case surges after year-end holidays, during summer months, and as activities resume in February and March. XBB.1.5 could amplify this seasonal pattern, particularly if it spreads efficiently among populations where earlier lineages like BQ.1—which caused a November surge in Brazil—had circulated.
The challenge in predicting wave severity is real. Mellanie Fontes-Dutra, a biomedical scientist and professor at Unisinos health school, cautioned that "if we create opportunities for the virus to circulate, it will take them, and we could find ourselves in more complicated situations." While experts do not expect a new wave to match the scale of the original Omicron surge last year, they emphasize that high viral circulation always carries risk. More cases bring more deaths and hospitalizations in their wake. A particular concern is the low booster vaccination rate among young adults and working-age Brazilians.
Defense against XBB.1.5 rests on several pillars. Vaccination, especially updated bivalent booster doses, remains critical. Early data suggest these newer vaccines generate neutralizing antibodies capable of offering greater protection against circulating Omicron variants, even accounting for their partial immune escape. Standard boosters, though not updated, still provide solid protection against severe disease. Beyond vaccination, experts call for building a "culture of respiratory hygiene" in Brazil—mask use in enclosed spaces and crowds, particularly for those with respiratory symptoms. People with underlying conditions, the elderly, and the unvaccinated must take heightened precautions. Spilki made a direct appeal for testing: "It is not enough to vaccinate, not enough to take other precautions. We must test, know when we need to isolate." Without testing, people remain unaware they carry the virus and unknowingly spread it further.
Notable Quotes
It is almost impossible that the new subvariant will not reach Brazil. The effects are what matter most to us.— Fernando Spilki, virologist at Feevale University
If we create opportunities for the virus to circulate, it will take them, and we could find ourselves in more complicated situations.— Mellanie Fontes-Dutra, biomedical scientist and professor at Unisinos
The Hearth Conversation Another angle on the story
Why did this variant get the nickname Kraken? Is it just marketing, or does the name tell us something real about what makes it dangerous?
The name captures something genuine about its nature. It's not just transmissible—it's transmissible in a way that slips past our existing defenses. The virus fixed a weakness in its parent strain and gained the ability to evade antibodies at the same time. That combination is what earned the mythical monster name. It's a virus that seems to come from nowhere and overwhelms you.
You mentioned that hospitalizations doubled in the U.S., but cases don't seem to be rising at the same rate. What does that gap tell us?
It tells us people have stopped testing. When you don't test, you don't know you're infected, so you don't report it. The hospitalizations and deaths are real—those are harder to hide—but the case numbers are invisible. It's like watching an iceberg where only the tip shows above water.
Brazil already had XBB circulating. So XBB.1.5 arriving isn't entirely new territory?
Right, but it's a crucial difference. XBB was less efficient at infecting cells. XBB.1.5 fixed that problem. So even though Brazilians may have some immunity from earlier exposure, this version is better at getting around it and better at spreading. It's the same family, but a more dangerous cousin.
The experts seem cautious about predicting how bad a new wave could be. Why is that uncertainty there?
Because it depends entirely on behavior. If people gather indoors, if testing drops, if vaccination rates stay low—the virus will exploit all of that. The variant's capability is one thing; what we do with our freedom is another. That's the part no one can predict.
What's the most concrete thing someone in Brazil should do right now, before the variant arrives?
Get boosted, especially with the updated bivalent vaccine if available. Wear a mask in crowded indoor spaces. And if you have any respiratory symptoms at all, test yourself. The scientists keep coming back to testing because it's the one thing that actually breaks the chain of spread.