Will BA.2 take off in the US?

I just ran across a recent post in the NYT by Carl Zimmer, a science writer who regularly writes for leading outlets. It opens with the following.

Given that opening, I expected an argument to back up the claim that “it doesn’t appear to have the capacity to drive a large new wave of infections.” Before addressing the argument, Zimmer discussed what we know about the variant, including how long it’s been around and how transmissible it is. About a third of the way through, Zimmer wrote, “there are a number of reasons that epidemiologists doubt that BA.2 will drive a massive new surge.”

“Here we go,” I thought. Zimmer is a reputable science writer, and he was about to show me why we don’t have much to worry about with this variant, so I was excited and hopeful. But there was no mention of who the epidemiologists were who had doubts about BA.2’s ability to spread in the US.

The first pillar in the argument was that “British health officials have compared the effect of vaccines against BA.1 and BA.2 infections. They’ve found little difference between the two subvariants. And in both, a booster shot provides fairly strong protection against infection and very strong protection against hospitalization.”

That sounds good, right? But there’s a problem here. The EU and UK have far higher uptake of boosters, and they’re getting clobbered with BA.2 right now.

Zimmer’s next pillar rests on the finding that “The BA.2 variant is vulnerable to antibodies made by the immune system after an earlier Omicron infection.”

This also sounds good, as there were more Omicron cases than any prior variant, but how many cases weren there? As the chart below shows, Omicron’s spread took off in December 2021 in the US.

Since the beginning of December, the US has officially recorded about 30 million cases. I assume it was significantly higher than the official number, but 30 million is less than 10% of the US population, and not all cases were Omicron during that time.

So a lot of people appear to have a high level of protection against this new subvariant. But even if we assume all of the people infected by Omicron (BA.1) did not have booster shots (that’s not the case), it seems a stretch to assume those two groups included even half the US population.

From here, things get a little weird. Having made two points arguing against BA.2’s ability to take off in the US, Zimmer jumps to severity.

The argument that’s being made here is about transmission. Severity is an important issue, but it is not directly relevant to the argument.

He then makes a point about the effectiveness of available treatments.

The effectiveness of treatments is an important matter in terms of severity, but it is not directly a matter of transmission. It’s possible that these treatments reduce transmission, but that case wasn’t made here. And as of November 2021, that was still an open question. (I recall claims of such, but I wasn’t able to find anything confirming the case. Please reach out if you’re aware of any evidence, and I’ll gladly update this.)

The final point in the article is that “BA.2’s ‘stealth variant’ nickname is outdated.”

The argument here is that tests struggle to detect BA.2, but now we ‘know’ that when a test does not detect BA.1 (the original Omicron variant), it’s likely to be a BA.2 case.

This is again not a matter of transmissibility/transmission. It is purely a matter of detection. Being able to detect the variant, or assume that you’ve detected it, seems a good thing, but if it’s not somehow reducing transmission, it’s irrelevant.

To recap: boosters work well against it, and having had Omicron (BA.1) provides strong protection against reinfection with BA.2 (at least in the short-term). There’s also some stuff about severity, the effectiveness of treatments, and our ability to detect (or assume we’ve detected) the variant.

That’s it. That’s the whole shooting match.

I’m not saying it’s time to raise the alarm, but if that’s all we’ve got, I’d be getting ready for the next wave and rethinking recent moves if I was at the CDC.

I'll leave you with the chart below, which shows the new confirmed cases per million people by income group. It has high-income nations trending up sharply and upper-middle-income nations trailing them, while lower-middle-income nations are trending down, and low-income nations remain flat. Unfortunately, Our World in Data does not provide the same income-based tracking for daily tests, so you’ll have to imagine what that might look like and what it might mean for this chart.