I’m just going to go ahead and say it right up front here: if you had certain expectations in May/June about how the pandemic was going to end in the US (or was even thinking it was over), you need to throw much of that mindset in the trash and start again because the Delta variant of SARS-CoV-2 has changed the game. I know this sucks to hear,1 but Delta is sufficiently different that we need to reset and stop assuming we can solely rely on the vaccines to stop Covid-19 from spreading. Ed Yong’s typically excellent piece on how delta has changed the pandemic’s endgame is helping me wrap my head around this.
But something is different now — the virus. “The models in late spring were pretty consistent that we were going to have a ‘normal’ summer,” Samuel Scarpino of the Rockefeller Foundation, who studies infectious-disease dynamics, told me. “Obviously, that’s not where we are.” In part, he says, people underestimated how transmissible Delta is, or what that would mean. The original SARS-CoV-2 virus had a basic reproduction number, or R0, of 2 to 3, meaning that each infected person spreads it to two or three people. Those are average figures: In practice, the virus spread in uneven bursts, with relatively few people infecting large clusters in super-spreading events. But the CDC estimates that Delta’s R0 lies between 5 and 9, which “is shockingly high,” Eleanor Murray, an epidemiologist at Boston University, told me. At that level, “its reliance on super-spreading events basically goes away,” Scarpino said.
In simple terms, many people who caught the original virus didn’t pass it to anyone, but most people who catch Delta create clusters of infection. That partly explains why cases have risen so explosively. It also means that the virus will almost certainly be a permanent part of our lives, even as vaccines blunt its ability to cause death and severe disease.
And a reminder, as we “argue over small measures” here in the US, that most of the world is in a much worse place:
Pandemics end. But this one is not yet over, and especially not globally. Just 16 percent of the world’s population is fully vaccinated. Many countries, where barely 1 percent of people have received a single dose, are “in for a tough year of either lockdowns or catastrophic epidemics,” Adam Kucharski, the infectious-disease modeler, told me. The U.S. and the U.K. are further along the path to endemicity, “but they’re not there yet, and that last slog is often the toughest,” he added. “I have limited sympathy for people who are arguing over small measures in rich countries when we have uncontrolled epidemics in large parts of the world.”
Where I think Yong’s piece stumbles a little is in its emphasis of the current vaccines’ protection against infection from Delta. As David Wallace-Wells explains in his piece Don’t Panic, But Breakthrough Cases May Be a Bigger Problem Than You’ve Been Told, vaccines still offer excellent protection against severe infection, hospitalization, and death, but there is evidence that breakthrough infections are more common than many public health officials are saying. The problem lies with the use of statistics from before vaccines and Delta were prevalent:
Almost all of these calculations about the share of breakthrough cases have been made using year-to-date 2021 data, which include several months before mass vaccination (when by definition vanishingly few breakthrough cases could have occurred) during which time the vast majority of the year’s total cases and deaths took place (during the winter surge). This is a corollary to the reassuring principle you might’ve heard, over the last few weeks, that as vaccination levels grow we would expect the percentage of vaccinated cases will, too — the implication being that we shouldn’t worry too much over panicked headlines about the relative share of vaccinated cases in a state or ICU but instead focus on the absolute number of those cases in making a judgment about vaccine protection across a population. This is true. But it also means that when vaccination levels were very low, there were inevitably very few breakthrough cases, too. That means that to calculate a prevalence ratio for cases or deaths using the full year’s data requires you to effectively divide a numerator of four months of data by a denominator of seven months of data. And because those first few brutal months of the year were exceptional ones that do not reflect anything like the present state of vaccination or the disease, they throw off the ratios even further. Two-thirds of 2021 cases and 80 percent of deaths came before April 1, when only 15 percent of the country was fully vaccinated, which means calculating year-to-date ratios means possibly underestimating the prevalence of breakthrough cases by a factor of three and breakthrough deaths by a factor of five. And if the ratios are calculated using data sets that end before the Delta surge, as many have been, that adds an additional distortion, since both breakthrough cases and severe illness among the vaccinated appear to be significantly more common with this variant than with previous ones.
Vaccines are still the best way to protect yourself and your community from Covid-19. The vaccines are still really good, better than we could have hoped for. But they’re not magic and with the rise of Delta (and potentially worse variants on the horizon if the virus is allowed to continue to spread unchecked and mutate), we need to keep doing the other things (masking, distancing, ventilation, etc.) in order to keep the virus in check and avoid lockdowns, school closings, outbreaks, and mass death. We’ve got the tools; we just need to summon the will and be in the right mindset.
Tags: Covid-19 David Wallace-Wells Ed Yong medicine science USA
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