The virus evolved faster than immunity could adapt
Duas novas sublinhagens do Omicron — BA.4 e BA.5 — estão reescrevendo o curso da pandemia em múltiplos continentes, encontrando brechas nas defesas imunológicas construídas ao longo de dois anos de infecções e vacinações. Não são necessariamente mais letais, mas sua capacidade de escapar da imunidade preexistente as torna mais ubíquas — e a ubiquidade, em escala suficiente, tem seu próprio peso em vidas. O que se observa no Brasil, em Portugal e na Europa é um lembrete de que o vírus não precisa se tornar mais feroz para se tornar, novamente, um problema coletivo.
- Em apenas quatro semanas, as sublinhagens BA.4 e BA.5 saltaram de 10% para 44% dos casos confirmados no Brasil, empurrando a média diária de infecções a níveis não vistos desde março.
- A média móvel de mortes voltou a 163 por dia — um patamar que o país não registrava desde o início de abril — e as hospitalizações crescem especialmente entre pessoas acima dos 60 anos.
- Testes laboratoriais confirmam que o soro de vacinados com três doses e de pessoas previamente infectadas neutraliza essas sublinhagens com eficácia significativamente menor, sobretudo à medida que a imunidade vacinal declina com o tempo.
- Portugal, onde BA.5 já domina mais de 90% dos casos, funciona como vitrine do que está por vir: reinfecções em alta, hospitalizações subindo, mas ainda abaixo dos picos anteriores do Omicron.
- Autoridades sanitárias europeias preveem que essas sublinhagens se tornarão dominantes no continente até o outono, e cientistas brasileiros voltam a recomendar o uso de máscaras em ambientes fechados como medida preventiva.
Duas sublinhagens do Omicron — BA.4 e BA.5 — identificadas pela primeira vez na África do Sul no início de 2022, tornaram-se o novo motor da pandemia em várias regiões do mundo. No Brasil, a transformação foi rápida: em meados de junho, essas variantes respondiam por quase metade de todos os novos casos, contra pouco mais de um décimo apenas quatro semanas antes. O país registrava 43 mil casos diários e uma média de 163 mortes por dia — números que remetiam aos momentos mais sombrios da primavera.
Portugal oferece um retrato adiantado do que essas sublinhagens são capazes. Com BA.5 dominando mais de 90% das infecções, o país viu crescer as hospitalizações e os internamentos em UTI, especialmente entre os mais velhos. Na Europa, o padrão se repete de país em país, e o Centro Europeu de Controle de Doenças projeta que essas sublinhagens dominarão o continente em semanas, intensificando a transmissão durante o verão e o outono.
O que distingue BA.4 e BA.5 não é maior letalidade, mas maior habilidade de escapar da imunidade — tanto a gerada por vacinas quanto a adquirida por infecções anteriores. Estudos laboratoriais mostram que o soro de pessoas com três doses de vacina neutraliza essas sublinhagens com eficácia reduzida, e o efeito se agrava com o passar do tempo desde a última dose. Isso explica a onda de reinfecções observada em Portugal e o avanço veloz das sublinhagens mesmo em populações com alta cobertura vacinal.
A África do Sul, onde a onda já passou, oferece algum alento: o virologista Tulio de Oliveira observou que o surto foi muito menos letal do que qualquer onda anterior, graças à imunidade acumulada e à capacidade hospitalar disponível no momento certo. O desafio, portanto, não está na ferocidade do vírus, mas na aritmética brutal de uma transmissão ampliada: mais casos, mesmo entre populações parcialmente protegidas, significam mais internações e mais mortes em números absolutos. O que vem a seguir depende menos da biologia do vírus e mais das escolhas coletivas que ainda estão por ser feitas.
Two new versions of the Omicron virus—BA.4 and BA.5—are reshaping the pandemic's trajectory across the globe. First spotted in South Africa in January and February, they have since become the dominant strains driving fresh waves of infection in Africa, Europe, and now Brazil, each region watching the same pattern unfold: cases climbing, hospitals filling, the virus finding its way past defenses that worked before.
In Brazil, the shift has been dramatic. Four weeks before mid-June, these subvariants accounted for just over one in ten confirmed cases. By early June, they represented nearly half of all new infections. The daily case count had climbed to 43,131—a figure not seen since early March. Over the week of June 5 to 11, the country recorded 292,000 new cases, approaching the 317,000 logged during the March surge. Deaths, too, were rising. The seven-day average of daily fatalities had reached 163, a threshold untouched since April's opening weeks.
Portugal offers a window into what happens when these subvariants take hold. There, BA.4 and BA.5 account for more than nine in ten new infections. The country has seen its hospitalization rates and intensive care admissions climb, particularly among people over sixty. Across Europe, the pattern is repeating. Austria, Belgium, Denmark, France, Germany, Italy, the Netherlands, Spain, and Sweden are all watching these subvariants gain ground. In Belgium, they represent roughly a quarter of new cases. Germany's public health institute reported them at just over twelve percent of infections in early June, though the older BA.2 still dominated at eighty-seven percent. The European Centre for Disease Prevention and Control predicts these newcomers will become the continent's dominant strains within weeks, likely driving case numbers higher through the summer and into autumn.
What makes BA.4 and BA.5 different is their architecture. Like all Omicron descendants, they carry mutations in the spike protein—the structure the virus uses to invade cells. But they carry additional mutations elsewhere in their genetic code. The practical effect is clear from laboratory work: blood serum from people vaccinated with three doses of Pfizer-Biontech or AstraZeneca proved less effective at neutralizing these new subvariants than it had been against earlier versions. The same held true for serum from people who had already been infected once. In other words, both vaccination and prior infection offer less protection against BA.4 and BA.5, especially as vaccine-induced immunity naturally declines over time. This explains why Portugal is seeing a surge in reinfections—people catching the virus again after previous bouts.
Yet there is a crucial distinction between transmissibility and severity. No evidence has emerged that BA.4 and BA.5 cause more serious illness than other Omicron subvariants. In Portugal, where BA.5 has nearly taken over, hospitalization rates, ICU admissions, and death counts stood below previous Omicron peaks as of June first, though they have begun climbing since. In South Africa, where the wave peaked in mid-May, virologist Tulio de Oliveira noted the outbreak was far less deadly than any previous wave—a difference he attributed to the population's accumulated immunity from prior infections and vaccination, combined with adequate hospital capacity when the surge began.
The calculus facing health authorities is therefore complex. These subvariants are not inherently more dangerous, but their superior ability to reinfect means more people will catch them. More cases, even among a vaccinated and previously infected population, can translate into more hospitalizations, more ICU admissions, and more deaths in absolute terms. Scientists and public health communicators in Brazil have begun urging people to resume precautions—masking in enclosed spaces, in particular—as a hedge against what may be coming. The European health agency has cautioned that the scale of the expected surge will depend on vaccination coverage, the timing of doses, and how much immunity lingers from earlier waves. What happens next depends not on the virus's inherent severity, but on how many people it reaches.
Citações Notáveis
The wave of BA.4 and BA.5 had a much, much less fatal impact than any of the previous waves— Tulio de Oliveira, virologist, University of KwaZulu-Natal
The subvariants may be responsible for a new wave in autumn— Karl Lauterbach, German Health Minister
A Conversa do Hearth Outra perspectiva sobre a história
Why did these subvariants emerge now, and what made them spread so much faster than what came before?
They didn't emerge because of anything we did wrong—they're just the virus doing what viruses do, mutating and testing which versions survive best. BA.4 and BA.5 happened to develop mutations that let them slip past immunity that had built up in the population. That's their edge. They're not new because they're more dangerous; they're new because they're better at reinfecting people.
So if someone had COVID in March and got vaccinated, they could still catch this?
Yes. That's what Portugal is seeing—people getting infected again. The virus has learned to dodge both the antibodies from vaccination and the antibodies from prior infection. It's not that the vaccines failed; it's that the virus evolved faster than immunity could adapt.
But you said they're not more severe. So why should anyone worry?
Because more cases means more hospitalizations, even if the percentage of people who get seriously ill stays the same. If ten times as many people catch it, ten times as many might end up in the hospital. That's the math that matters for a healthcare system.
What's the difference between what happened in South Africa and what's happening in Europe now?
Timing and capacity. South Africa had high population immunity already built up, and hospitals had beds ready when the wave hit. Europe is watching it happen in real time and trying to prepare. The virus itself is the same; the context is different.
Is there anything that actually stops these subvariants?
Not stops, exactly. Vaccination still reduces severe illness. Prior infection still offers some protection. Masking in crowded indoor spaces still works. But nothing makes you immune to reinfection. The goal now is to slow spread and protect the most vulnerable—people over sixty, the immunocompromised—while the virus circulates.