Thread by @dwallacewells

“Pandemic anxiety has turned lately to the question of viral evolution—the possibility that the disease might be outracing our efforts to contain it.” Of all the new strains, the Brazilian variant may be most concerning. (1/x) nymag.com/intelligencer/…

“In the Amazonian city of Manaus, where antibodies had been previously estimated in 76% of the population, there has been a horrifying and deadly dramatic second wave, right in the middle of Brazilian summer in a place believed to have already developed true herd immunity.”

“A new ‘Comment’ published Wednesday in the Lancet surveys what we know about the Manaus variant, and offers four possible explanations for what has happened there. None of them are good. Three are quite terrifying.”

“The first possible explanation is the most optimistic one: Perhaps that 76 percent finding was wrong, and many fewer people in the city had been exposed to the disease than that much-talked-about study suggested.”

“Even before the second wave, there were some indications that the estimate — which was based on mathematical modeling on top of a basic sample set — might have been high: 76 percent would have been above a crudely estimated herd-immunity threshold of 67 percent.”

“But herd-immunity estimates are rarely precise; even when you have the numbers precisely right, there is always a risk of ‘overshoot,’ and nearby Iquitos, in Peru, registered a similar attack rate of 70 percent.”

“The true observed seroprevalence in the earlier survey, which was adjusted upward to reflect antibody waning, was 52 percent, and even taking that lower-bound estimate, should have produced significant-enough protection to prevent an outbreak like the city’s second wave.”

“The second possible explanation is that the immunity measured by that earlier survey may already have waned — meaning that at least some significant group of those people estimated to have immunity in October had become vulnerable to infection again.”

“Among other things, this would suggest that at least some of those infected in early waves not just in Wuhan, Lombardy, New York, and London may be again vulnerable to infection already.”

“A third possible explanation is that the new variant, like those discovered recently in the U.K., South Africa, and California, is more transmissible than the strains that have dominated the pandemic thus far.”

“This would mean both that the level of acquired immunity in the population would have to be higher to offer herd immunity protection — perhaps north of 80 percent — and that the disease might be working much more quickly through that relatively small slice of the population.”

“The scariest of the possible explanations is even worse — that the new strain has achieved a more total ‘immune escape,’ meaning that it could evade antibodies produced by exposure in the first wave and infect again, even those people who’d mounted a robust immune response.”

“This is scarier than the possibility of waning transmission, because at least under that theory, antibodies offer protection for a period of time; and it is scarier than enhanced virulence, because it doesn’t just mean that those without antibodies are at heightened risk.”

“Instead, it would mean that existing antibodies could offer little protection, or perhaps no protection at all, with the disease progressing through the community a second time just as quickly and devastatingly as it did the first.”

“In other words, in theory at least, it could mean reducing what appeared to be a well-protected community into a virgin population—and would represent a threat of that kind to any community, anywhere in the world, should the Brazilian variant arrive, as it now has in Minnesota.”

“These hypotheses are not mutually exclusive, the authors point out — the new surge could be multiply determined. But whatever is driving it, the picture is scary.”

“A hospital that was overwhelmed in ten days in the spring became overwhelmed, this time, in just 24 hours, the Washington Post reports. Hospital patients arrived at the hospital sicker than in the first wave, ‘their lungs chewed up with disease.’”

“Local doctors insist the disease is not just more transmissible now but also more severe — and the data show that the epidemic is bigger this time than the first wave.”

“As anxiety about the new variants has mounted, those hoping to strike a tone of reassurance have pointed to evidence suggesting that, while vaccines may produce a somewhat less robust response against the new variants, they did produce what appears to be a sufficient response.”

“But pull back and the picture grows more concerning — and indeed reveals our focus on vaccine efficacy as a bit of global North narcissism.”

“A forecast published this week by the Economist Intelligence Unit suggested that most of the world’s poor countries are unlikely to reach mass immunization through vaccination before 2024 at the earliest, and may never get there.”

“If the Manaus experience is explained by waning antibodies, that could mean that nations in the developing world would pass through six or eight full pandemic cycles before vaccines arrive at scale.”

“If it is explained by immune escape, the path forward would not necessarily be quite so brutal...”

“It would mean that this variant evolved to evade previous antibody protection, and would tragically reset the clock on all naturally acquired immunity wherever it traveled, but in the absence of additional new strains populations would have to start from scratch...”

“...but could build up natural immunity over time.”

“Of course there will almost certainly be more variants coming over those next three years as well.” (X/x)