Influenza
Transmission
🤧 I just had influenza, so spent some time looking up information about incubation periods and contagiousness to figure out how to keep Spouse from getting sick. O. My. Word. There is so much information that is just plain wrong out there!
Almost every web page I visited said that influenza was passed by droplets (which fall to the ground within about six feet of people coughing/sneeezing) and fomites (i.e. surfaces). This is not true: the biggest transmission route is via aerosols that travel long distances through the air, just like with COVID-19 (see this web page for more, with references).
How can “everybody” be so wrong? Welll, read the book Air-Borne by Carl Zimmer if you want a deep dive, or this Wired article (2021-05-13) for a shorter version (but still long) but here’s a quick summary:
- Once upon a time, everybody thought that disease was caused by bad air, AKA miasma.
- Eventually people figured out that disease was caused by germs, but there was a big scientific fight about it — as there is every time dogma gets changed. This meant that the pro-germ people went hard after anybody who said anything even slightly pro-miasma — and aerosol transmission sounds too uncomfortably like “miasma” to let it go unchallenged.
- A guy named Wells did some experiments in the 1940s where rabbits exposed to tuburculosis particles in a mist of particles under 5 microns all got sick; those who got a mist of TB particles over 5 microns in size did not get sick.
- It appears that CDC picked “5 microns” as the important size for disease transmission… but somehow that got interpreted as disease being an issue for particles over 5 microns.
- They thought that 5 micron particles would fall down quickly. (Spoiler: they do not.)
- There was a lot of institutional resistance to changing the advice that respiratory diseases could spread over long distances via aerosols. Part of it was simply that people had been trained on droplet theory, had it drilled into them, taken exams that required that answer on tests, etc. But part of it is that acknowledging long-distance transmission required a lot more work from institutions. If droplet theory is correct, then all your customers/patients/workers need to do is stand six feet apart, done. If respiratory diseases transmit through the air over long distances, then you need to do a shitton of work to make the air safer (or make everybody wear a mask, which a lot of customers/patients/staff don’t like doing).
- It’s scary to think about things that can stealthily infect you through the air! It’s difficult to protect yourself from invisible things!
The dogma about COVID-19 transmission now appears to accept that aerosol transmission is a risk. However, that shift doesn’t seem to have made it to influenza resources, and I’m not sure why: perhaps the influenza pages haven’t been updated since before the pandemic?
There’s also a huge overemphasis on washing hands — both for COVID-19 and for influenza. While it is possible to pick up diseases from surfaces, it’s not nearly as big a threat as airborne transmission. (See here (2025-05-21), here, here, and here (2018-08-09).)
Vaccines
Something that I also knew intellectually, but had avoided thinking about, is that almost all socialized-medicine governments provide influenza vaccines to everybody for free, but there are lots who only provide COVID-19 vaccines to limited, more vulnerable populations — despite the fact that COVID-19 is still more deadly than flu (see below). Not only that, in places where people can get them equally, many more people get the flu shot than the COVID-19 shot. Why do more people get flu than COVID-19 shots? I think there are multiple reasons:
- People have been getting flu shots for a long time. Your parents probably got flu shots. This means that people are already in the habit of getting flu shots.
- Flu shots are cheap; COVID-19 shots are expensive. This means that the governmental risk trade-off looks different (especially if they don’t take into account the long-term elevated risk of many things — which they don’t, for reasons I talked a lot about in this post (2025-08-11)).
- A lot of people are wary about the mRNA technology.
- COVID-19 vaccines frequently make you feel quite bad for a day. (FYI: the more COVID-19 vaccines I get, the less bad I feel.)
- COVID-19 vaccines wear off, so you have to keep getting new ones.
- Some people don’t know that, so they think that they’ve gotten enough COVID-19 vaccines and don’t need more.
- Some people do know that and so figure why bother?
- Note: flu vaccines wear off too, but flu only circulates for a few months in the winter, so getting a shot once per year is a more reasonable thing to do.
COVID-19
Transmission
These Christmas cookies are shaped like something that people traditionally share a lot of during the holidays:
COVID-Related Excess Death and Sickness
☠️ COVID-19 is not the flu! This paper from South Korea (2025-12-17) reports that people who had a COVID-19 infection were 76% more likely to die within 30 days than people who had an influenza infection.
😴 This paper from USA (2025-12-18) reports that Long COVID messes up your sleep. People with Long COVID had a 3.27 times higher risk of sleeping less than six hours per night about 1.5 years after infection than people who’d had COVID infections but not Long COVID. At three years, the relative risk compared to controls dropped, but was still 1.91 times higher.
Vaccines
💉 This paper from USA (2025-12-24) reports that the vaccine effectiveness of the KP.2 booster from August 2024 to January 2025 among veterans was not-great against everything except death and declined over time, compared to veterans who did not get a booster. The vaccine effectiveness was:
| against | at 60 days | at 90 days | at 120 days |
| infection | 31.28% | 25.81% | 22.44% |
| ED/UC visit | 34.40% | 29.19% | 25.71% |
| hospitalization | 37.39% | 28.98% | 22.52% |
| death | 75.02% | 71.02% | 63.08% |
Remember, though, that the comparison population might have gotten some immunity via infection. Vaccinations are much safer than infections.
💉 This paper from Canada (2025-12-15) reports that vaccination is a very good thing for pregnant people. Vaccination effectiveness was:
| against | during Delta | during Omicron |
| hospitalization | 62% | 62% |
| ICU admission | 90% | 90% |
| pre-term birth | 20% | 36% |
The high effectiveness held up after adjusting for comorbidity. The unvaccinated had a 2.43x higher adjusted risk than the vaccinated during Delta, which rose to 3.82x higher adjusted risk during Omicron.
💉 This press release from the World Health Organization (2025-12-18) says that the next vaccines should use LP.8.1 as their base.
Treatments
💊 This paper from Hong Kong (2025-12-21) reports that hospitalized patients who were given Paxlovid had a significantly lower risk of many long-term cardiovascular complications than controls. Patients who got molnupiravir had a short-term reduction in cardiovascular issues, but not a long-term one.
H5N1
Transmission
🐦⬛🐄🤧 This press release from USA (2025-12-19) reports that there was a new “spillover event” from birds to cows in Wisconsin. (This means that cows got infected by wild birds, as opposed to cows getting infected by other cows.) This is the fourth independent birds-to-cows spillover event in the US.
Measles
Transmission
According to the Government of Canada Measles and Rubella Monitoring Report (updated 2025-12-22), in the week ending 13 December, the following jurisdictions had the following number of measles cases:
- Canada: 24;
- Manitoba: 10;
- BC: 7;
- Alberta: 6;
- Quebec: 1.