Locator: 49964FLU.
Because of AI (chatbots), I have never felt so comfortable with my understanding of seasonal flu as I do now -- influenza A and B.
So, generally speaking there are two waves of influenza every season between October and May.
Today, a reply from Google Gemini said there were many reasons for those two waves, the lead reason being the "drift" of the antigenic strain over the season.
Google Gemini then said, as an example, the strain would drift from H3N1 to H1N2.
In fact, that is so wrong. First of all, H3N1 and H1N2 are not strains, but rather sub-types.
Influenza:
- A, B, C, D: the four types of influenza
- type D, only recently discovered, affects cattle, never affects humans (not yet, and probably never)
- type A: multiple sub-types, not strains; determined by surface antigens; HxNx; only two surface antigens: H and N;
- type B: has no subtypes, only two lineages, which further branch into specific strains; the two lineages: B/Yamagata and B/Victoria; B/Yamagata has not been seen since 2000 (interesting, the year of Covid-19)
- influenza B changes much more slowly and primarily affects humans
So, now, with that information we can follow "antigenic drift" for the rest of the 2025 - 2026 seasonal flu season.
First, week four of 2026:
- where are we?
- end of the first wave
- beginning of the second wave, just beginning; off to a slow start
- overall, all influenza (A and B) has decreased significantly since the start of the season, last autumn, 2025, but is now picking up slowly;
- since last week:
- percent of influenza A decreased week/week and influenza B increased slightly (again, as percentages but also as raw numbers);
- now this is the interesting part:
- earlier Google Gemini said the antigenic drift was due to subtype drift (H, N) so let's check that drift.
- subtyping (remember, the type is A or B) has remained relatively unchanged for Type A
- H1N1 (pdm09) [see below]:
- September 28, 2025 (week 40): 11.6%
- Week 4, 2026: 14.5%
- H3N2:
- September 28, 2025 (week 40): 88.4%
- Week 4, 2026: 85.7%
- H3N2v: 0% at week 40 (2025) and week (2026) [v = variant; usually swine]
- H5: 0% at week 40 (2025) and week (2026) [A(H5) = avian]. See link.
So, gradual drift to H1N1 from H3N2.
This year's trivalent flu vaccine:
- H1N1, H3N2, and B/Victoria.
I finally get it.
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H1N1(pdm09)
H1N1 pandemic 2009
This virus caused the first influenza pandemic of the 21st century and has continued to circulate seasonally since 2009.
Covid-19: after months of reading about influenza A and Covid-19, I am convinced that Covid-19 was an anomaly, and clearly due to "unusual" human-non-human interaction in the late summer of 2020 in China.
Whether it was "an escape" from a lab or naturally occurring in a Chinese market, or somehow a combination of the two, is still debated. To say that researchers were not involved strains credibility, the fact that is first broke out where China's main bio-threats lab is located and researchers in China had so much of this sorted out so quickly.
My hunch: Chinese researchers (like American researchers) were aggressively monitoring avian/swine viruses in those Chinese markets, and either discovered a "new" virus or "developed" a new virus.
My hunch: like Spanish flu (1918), Covid-19 was simply a previously-unseen flu virus.
Interestingly, Spanish flu was caused by an H1N1 subtype. It evolved and circulated for decades.
Descendants of the 1918 virus continued to cause seasonal influenza, with the human H1N1 lineage circulating until around 1957 before reappearing in 1977.
The surface antigens of Covid-19 and influenza A are completely different and there is no antigenic cross reactivity.
- Influenza A: two membrane surface antigens, H and N.
- a segmented genome of eight separate negative-sense RNA strands
- Covid-19: surface covered with Spike (S) glycoproteins (crown or corona); binds to ACE2 receptor
- a single-stranded non-segmented positive-sense RNA; it encodes 11 - 12 functional proteiin-coding genes.
This is just one of many blogs on influenza this season.
