I noted recently that claims about exceptionally high rates of RSV this year, caused by "immunity debt" and explaining the high number of children in hospital, is an empirical claim that requires data. Well, we now have this for Canada thanks to @Wikisteff (follow him btw!). 🧵
Here is a plot of RSV rates since winter 2013/2014. As you can see, it's a very regular seasonal pattern for all the years up to the start of the COVID pandemic. There was essentially no RSV two years ago when schools were closed (winter 2020/2021).
And it's not just RSV. There was almost no flu or colds caused by other coronaviruses (not SARS2) two years ago either.
So, we can conclude two things right away: 1) mitigations worked extremely well and absolutely crushed respiratory virus transmission, and) the first assumption of "immunity debt" holds, namely that there was a season without kids being infected with RSV or flu.
BUT, look at last year. Winter 2021/2022 was a record season for RSV. It is simply not accurate that we are seeing three years' worth of RSV cases this year. RSV was back last year after many mitigations were lifted.
Last year, there were lots of cases of RSV but hospitals were not overwhelmed like they are right now. This year, RSV season has started early but the case numbers are not exceptionally high yet. Still, many kids are in the hospital already.
So, this doesn't fit with the simple "immunity debt" hypothesis. Something else seems to be going on. Of course, high rates of severe infection without more cases is consistent with the "immunity theft" hypothesis in which past COVID infection impairs immune function.
But there is another interesting observation pointed out by @Prassas, namely that flu was NOT back last year the way RSV was. Is there something about RSV and flu co-infections that matters? Immunity debt to flu but not RSV? Is flu more severe this year?
We still don't know what exactly is happening. What is pretty clear, though, is that assuming that it's simply "immunity debt" after two years of no RSV infections is false in Canada. This is why we need to test multiple hypotheses and why we need data, not just-so stories.
In the meantime, we *know* that mitigations work against the viruses that are leading to kids becoming very ill and pediatric hospitals being overwhelmed. Whatever the explanation, the right thing to do *right now* is to reduce transmission of these viruses in children. #MaskUp
Again, huge thank you to @Wikisteff for the data sleuthing -- this is exactly what we need. Also, as he noted:
For a bit more on "immunity debt" vs. "immunity theft" (the latter being only a slightly modified-for-catchiness version of @FurnessColin's "immunity robbery").
Don't forget to check out this fantastic discussion on @TheAgenda. Note that a couple of the claims made by Dr. McGeer (three years of RSV all at once after two years without, this only being a problem with pediatric hospitals in Canada) are not accurate.
It bears noting that there *is* a mechanism by which COVID infection can impair defence against RSV.
The best we get now is *relative* lows. Here are numbers of hospital patients with COVID in Canada. It's as low as it has been since the first Omicron wave (early 2022), on par with the relative lull of mid-summer 2023. But still much higher than summer 2020 and summer 2021.
*Maybe* it will continue to drop as thr weather warms and if there are no new major variants that displace JN.1* in the meantime (fingers crossed, and wastewater signal is low), but the reality is that the baseline has never come back down in Canada post-Omicron.
Relative lows do not mean no risk, they mean less risk. If you've been putting off doing things while cases were higher, a relative low is a better (but again, not risk-free) time to do them than during a relative high, obviously.
1. Israeli real estate companies held Jews-only events to sell land in Israel and contested (Jerusalem) or occupied (West Bank) territories in Palestine.
Note that some of the events are taking place in synagogues and some include properties that are within the illegally occupied West Bank. Other events have been held at public venues.
Now that Pirola clan (BA.2.86 and descendants, most notably JN.1*) is the dominant variant lineage globally, the question arises as to whether it might undergo recombination with earlier XBB lineages.
Yep. Already has.
🧵
So far...
Pirola x Arcturus:
XDK = JN.1.1.1 x XBB.1.16.11
Pirola x Eris:
XDD = JN.1 x EG.5.1.1
XDS = JN.3.2.1 x EG.5.1.3
Pirola x Kraken:
XDN = JN.1. x JD.1*
XDR = JN.1.1 x JD.1.1.1
Here are some excellent threads about more highly divergent BA.2 lineage variants showing up after having evolved within a single host with a chronic infection. Within-host evolution is going to be an increasingly important issue.