Last week I wrote about one of the central mysteries of the Omicron wave. It seems certain at this point that infection by the new variant produces much milder illness than Delta, which is nice but doesn’t matter much unless it also confers immunity from Delta. Some scientists worry that the two strains are sufficiently distinct that catching one doesn’t prime your immune system to neutralize the other. That could mean a “twindemic” of Delta and Omicron, in which the latter blazes across America, disappears, and then the former starts spreading again. Including among people who had Omicron.

The best-case scenario, the one in which Omicron is actually a blessing in disguise, is if it’s way milder and generates cross-immunity to Delta. Not all COVID variants do.

But according to researchers in South Africa, this one does. To some degree, at least.

The graph on the right is key. The sample for the study was tiny, as it was conducted quickly to get a sense of what infection by Omicron might mean for the prevalence of Delta worldwide. Scientists took blood from people who’d been infected by the new variant and tested their antibodies against both Omicron and Delta. Result: Their ability to neutralize Omicron had increased 14-fold — but their ability to neutralize Delta had also increased more than four-fold. Essentially, catching Omicron “boosted” them against both strains.

That’s a lucky break since, per the study, some strains don’t confer much immunity against others.

The ability of one variant to elicit immunity which can cross-neutralize another variant varies by variant. Immunity elicited by Delta infection does not cross-neutralize Beta virus and Beta elicited immunity does not cross-neutralize Delta well. However, participants in this study have likely been previously infected, and more than half were vaccinated. Therefore, it is unclear if what we observe is effective cross-neutralization of Delta virus by Omicron elicited antibodies, or activation of antibody immunity from previous infection and/or vaccination.

These results are consistent with Omicron displacing the Delta variant, since it can elicit immunity which neutralizes Delta making re-infection with Delta less likely. In contrast, Omicron escapes neutralizing immunity elicited by Delta and therefore may re-infect Delta infected individuals. The implications of such displacement would depend on whether Omicron is indeed less pathogenic than Delta. If so, then the incidence of Covid-19 severe disease would be reduced and the infection may shift to become less disruptive to individuals and society.

Note the bit about how all participants in the study were probably infected previously and then some were later vaccinated. Those people had hybrid immunity, the gold standard in being able to neutralize new strains of COVID. Whether those without hybrid immunity would neutralize Delta as well as they did is anyone’s guess but presumably a third vaccine dose helps close the gap. Either way, if this study holds up, it means Omicron is effectively vaccinating or boosting a huge number of Americans against Delta, which may help drive that deadlier strain to extinction. If what we’re left with at the end of the current wave is a pandemic that produces data like this…

…then we’re in a surprisingly hopeful place. Maybe hopeful enough to get back to normal? Even some scientists are daring to consider the possibility:

Some countries are still resisting. Israel has begun to test a fourth(!) dose of the vaccine as immunity from the third dose wanes, but that comes with two catches. One is that it’s not clear that additional doses will do anything except provide a temporary surge of antibodies that’ll reduce transmission of the virus briefly without conferring any durable benefit. Would a fourth dose do anything meaningful to enhance the immune system’s ability to respond quickly to infection and produce more sophisticated antibodies against new variants?

The second catch is a big one. Extra doses in short order might actually impair the immune response.

The panel of experts advising the Israeli government on the pandemic recognized that uncertainty, but on Tuesday it recommended giving a fourth dose, concluding that the potential benefits outweighed the risks. It pointed to signs of waning immunity a few months after the third shot, and said that any delay in additional doses might prove too late to protect those most at risk.

But some scientists warned that the plan could backfire, because too many shots might cause a sort of immune system fatigue, compromising the body’s ability to fight the coronavirus. A few members of the government’s advisory panel raised that concern with respect to the elderly, according to a written summary of the discussion obtained by The New York Times.

If Omicron isn’t killing people and really does seem to be crowding out Delta, why not roll with it for a few months while an Omicron-specific booster is developed for later next year?

I’ll leave you with two tweets, one of Ron Johnson asking a stupid question and the other demonstrating why it’s stupid.

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