David Wallace-Wells writes:

The term itself, perhaps, is a problem. “Breakthrough” sounds bad — implying an immune-escape mutation, likely rare, and therefore alarming.

The vaccines were never tested to prevent transmission, only symptomatic disease, and those who knew the science expected, from the outset, that we would see some number of such cases, and that they would be, overwhelmingly, mild. But Delta appears to have changed things. Not everything: The vaccines are working to suppress severe outcomes from COVID infection — according to a New York Times analysis, by more than a factor of 100 for some states, and at least fivefold for even the states where the effect has been most muted. That is, by the standards of historical vaccines, game-changingly well. But most of the data in that analysis comes from before the arrival of the Delta variant, and during the current surge there does seem to be considerably more “leakage” in the protection that vaccines offer against pandemic spread than has widely been acknowledged. While more severe breakthrough cases remain, in relative terms, very rare, we may be seeing a rise in those numbers with Delta, as well.

Over the last few weeks, in the wake of an attention-getting internal CDC presentation on the severity of the current wave, we’ve heard a lot — from epidemiologists, public-health officials, journalists like me — about how the leaked slides lacked context, implying a much scarier near-term future than was really suggested by the data, which showed that vaccines were working, that breakthrough cases remained rare and mild, that the pandemic was now largely a pandemic of the unvaccinated. On July 30, the Kaiser Family Foundation published a comprehensive-seeming report, much passed-around, which compiled partial breakthrough data from 24 states and the District of Columbia, and declared that the relative risk to the vaccinated of infection, hospitalization, and death was close to — or mathematically equal to — zero, and that in almost all states only about one percent of identified cases were breakthrough events.Their top-line findings: Less than one percent of vaccinated people have gotten confirmed breakthrough infections, and that the rate of both deaths and hospitalizations among the vaccinated were, effectively, zero. This reading was echoed by the later Times analysis, and itself echoed earlier reassuring statements by Anthony Fauci, that 99.2 percent of deaths in June were unvaccinated people, and by Surgeon General Vivek Murthy, that, as of July 18, “99.5 percent of COVID deaths are among the unvaccinated.”

These readings are, directionally, correct: The vaccines are performing admirably, particularly in protecting people from getting very sick. The current, bleak Delta wave is being driven primarily by cases in the unvaccinated, and the best tool in attacking the pandemic is more vaccination — a very powerful tool indeed. But nevertheless a closer look at the data reveals that some of the public-health communication may be overstating the vaccine effect on transmission and understating the scale and risk of breakthrough infections, which, while far from predominant, do appear prevalent enough to be helping shape the course of the disease. [Continue reading…]