The U.S. remains at 9 new COVID-19 cases per 100K per day, unchanged from a week ago. The different regions of the U.S. diverge, with continued new-case increases on the East Coast offset by declines in the South Central and Pacific regions.
That said, even though the U.S. curve hasn’t turned upwards, this is starting to look like every other inflection point on the curve. As the individual regions go their own separate ways, the “strands” that form the graph appear to be unraveling. Historically, that’s been a strong signal that the U.S. curve is likely to make a change in direction.
Data source for this and other graphs of new case counts: Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 4/5/2022, from https://github.com/nytimes/covid-19-data.” The NY Times U.S. tracking page may be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html
Dud-of-Omicron
At this point, I think we can dismiss son-of-Omicron (BA.2) as a serious threat in the U.S. The CDC reports that BA.2 accounted for almost three-quarters of new cases, as of the week ending 4/2/2022. By eye, there’s no correlation between regions with high BA.2. load and regions with more rapid new case growth. Whatever BA.2 would have done, it’s already done it. And it doesn’t appear to have done much.
Source: CDC COVID data tracker, accessed 4/5/2022
Flu-rithmetic: Why no flu, two years running.
This section started off with some fact-finding about the need for a second COVID-19 booster. I haven’t even thought that second booster yet because, as noted in prior posts, right now, I think my risk of hospitalization or death from COVID-19 is less than that for typical seasonal flu.
Which led me to look at current flu hospitalizations. Wherein I discovered that, once again, we aren’t really having a flu season this year. For the second year in a row.
Probably the best way to see just how mild this flu season was is to look at the rate of hospitalization for flu, relative to recent past seasons.
Source: CDC weekly influenza report, accessed 4/5/2022. Notes in red are mine.
Not quite as low as the missing flu season of 2020-2021, but pretty close.
Other indicators would give qualitatively similar results. For example, consistent with almost no flu hospitalizations for the past two seasons, there have been almost no deaths attributed to flu. That’s shown in the chart below, which combines deaths attributed to flu, pneumonia, and COVID-19. I’ve added notes in green to point out what’s missing from the last two flu seasons.
Source: CDC weekly influenza report, accessed 4/5/2022. Notes in green are mine.
It finally dawned on me this morning that I understand what’s driving this. And it’s just math.
Here’s the conundrum. These two successive years of exceptionally low flu rates — both here and in most of (e.g.) the northern hemisphere — are surely attributable to COVID-19 hygiene. But note that while those practices, such as mask-wearing, plausibly contributed to some containment of the spread of COVID-19, those appear to have stopped flu in its tracks?
How can the same set of practices have some modest effect on COVID-19, but absolutely devastate the spread of flu? Why aren’t we seeing just a moderation of the flu season, proportionate to the moderating impact that this hygiene had on the spread of COVID-19?
Is that an unexpected or an expected result? Answer: In hindsight, this is totally expected. Here’s why.
My best guess, based on an analysis I did last year, is that the total effect of all the COVID-19 hygiene practices in place at that time was to interrupt about half the chains of disease transmission. FWIW, that was back-solved from the observed rates of disease spread, and the stated r-nought of the strain of COVID-19 that was then prevalent. I’d also say that’s roughly consistent with studies of the impact of mask use on reducing the dose of aerosol particles inhaled.
If the R-nought of Omicron is 14 — if each infected person would infect 14 others if no protections were taken — then cutting that in half merely cuts the rate of disease spread a bit. You’d get an “R-effective” of 7: Every infected individual would only infect an average of seven others. That reduces what would have been a catastrophe to a mere crisis, but it doesn’t come close to ending the spread of disease. That is, it doesn’t come close to reducing the R-effective to less than 1.0, so that each infected person infects fewer than one near individual on average.
Here’s the key fact: The R-nought of typical seasonal flu is somewhere around 1.3. (Reference). And at that level, interrupting somewhere around half the chains of disease transmission is more than adequate to keep the epidemic in check.
The intense levels of COVID-19 hygiene prevailing during last year’s flu season appear to have been adequate to prevent almost all epidemic spread of seasonal flu. This year, even the less intense remnants of COVID-19 hygiene still in place for most of this season should have been easily enough to drive the R-effective for seasonal flu below 1.0.
The lack of a flu season for two years running — despite an ongoing COVID-19 season — isn’t luck. It’s just math. It’s a consequence of the lower baseline infectiousness of seasonal flu. The set of actions that merely makes a dent in COVID-19 transmission is more than adequate to stop epidemic spread of flu entirely, or nearly so.
As an afterthought, I have to say that the practice of wearing medical masks during flu and cold season — common in Asian countries but virtually unheard-of in the U.S. — is starting to look pretty smart. In hindsight, it seems like even a moderate amount of mask use during flu season might be enough to prevent the epidemic spread of flu that we have been accustomed to.
Second booster?
I haven’t gotten a second COVID-19 vaccine booster shot yet. In fact, I haven’t really even thought about it. That’s because the current level of U.S. new cases is low enough that I judge my risk of serious illness from COVID-19 is less than the same risk from typical seasonal flu. (Which is why I ended up looking at the current year’s flu season, above, and found out that this year isn’t typical.)
I went to find the CDC’s and FDA’s evidence in favor of getting a second booster shot now. I was less than impressed with their logic. In fact, I’d go so far as to say that they didn’t really do the right arithmetic. They seem to have focused on the immunity of a typical individual. There is evidence that immunity fades over time, particularly in the elderly. But the amount of harm avoided by vaccination is the product of individual immunity and prevalence of disease in the community.
Just to be clear, I don’t have any immunity to (say) cholera. Yet I’m not leaping at the opportunity to get a cholera vaccine. In fact, nobody recommends that I get one, despite my total and complete lack of immunity. That’s because my likelihood of exposure to it is nil, unless I travel overseas to a region where it is endemic.
And, to cut to the chase, my opinion is that immunity is not waning fast enough, and community prevalence is not high enough, for me to want to get that second booster right now.
It’s an inopportune time for it. I’d rather wait until we see evidence of the next wave of COVID-19 in the U.S. For one thing, you have to wait four months between booster shots. For another thing, if I get a second shot, there is as of yet no authorization for a third.
The upshot is that if I go for the 2nd booster now, I’m not really sure what my opportunities will be in (say) this October. So far, with two winters, we’ve had two winter waves of COVID. If it’s looking like we’re headed for one this winter, and no new evidence arises showing rapidly waning protection against severe disease, then that’s when I’ll get that second booster.
If I were a truly high-risk individual — had some significant risk factors, say, or worked in a setting where exposure was unavoidable — I’d probably go for it now. But as a safely retired suburbanite, still wearing a mask in crowded public areas, with fewer than 10 new cases per 100K per day in my area, no, I’ll pass for the time being.
So, what’s the evidence in favor? Looking at the FDA’s authorization statement, near as I can tell, the entire body of evidence in favor of effectiveness of a 2nd booster comes from a study of a non-randomized set of observations on health care workers in one location in Israel. There, the 2nd booster raised antibody titers against COVID-19. (You can read that here, on the FDA website).
In other words, near as I can tell, the evidence, as cited by the FDA, shows that the second booster does something. It raises antibody titers. But that appears to be all the evidence they have in favor of a second booster shot.
That’s really not much. It would be a surprise if the booster shot didn’t increase circulating antibodies. The extent to which that second booster shot (e.g.) reduced COVID-19 hospitalizations is unknown.
Near as I can tell, all the rest of the information regarding potential effectiveness of a second booster is purely observational data. That is, the individuals choosing to get a second booster shot had a markedly lower rate of deaths from COVID-19 compares to those who did not choose to get a second shot. (References in this reporting.) But that’s observational data, not a randomized trial. It’s a good bet that those who opted for the second booster were more health-conscious and cautious than those who did not.
Balanced against that is some evidence that immunity from the first booster fades noticeably after four months. That’s also observational data, but at least it’s consistent with what was observed with the main series of vaccinations. The cited data (from CDC) was that the third shot was 91% effective in avoiding COVID-19 hospitalizations in the first two months, falling to just 78% effective in at some unspecified time interval exceeding four months.
(That’s based on a “test negative” analysis, where they take all the persons hospitalized for a given set of conditions, COVID among them, and attempt to infer the effectiveness of the COVID-19 vaccine based on vaccination rates among the COVID-19 hospitalizations versus the persons hospitalized for some other cause. Just to be clear, that’s not the same as conducting a randomized clinical trial. Putting aside all other aspects of methods, if the most vulnerable populations were vaccinated first, the correlation of the ordering of the vaccination cohorts based on risk, with time-since-vaccination, could affect the results. In other words, plausibly the population with the most well-aged booster shots is also the population with the highest associated risk factors.)
That said, let me try to put this in perspective.
A second booster will give you additional protection. It’s hard to say just how much more protection you get. But more. And the preponderance of evidence suggests that your overall level of protection fades materially at some point more than four months following your last booster.
But you should balance that against the odds of severe illness.
Right now, in Virginia, for my age group, we are seeing about 2 COVID-19 hospitalizations per 100,000 population per day. (That’s from the N.Y times COVID maps.) I’ve already gone through the exercise of showing that the majority of Virginia COVID hospitalizations are among the un-vaccinated. As a vaccinated-and-boostered person, not living in one of the hotspot counties of Virginia, I’d have to guess that my odds of being hospitalized for COVID on any given day are somewhere around one-in-a-quarter-million.
Translating that to an annual rate, that’s about a 0.1% chance.
And by getting a booster now, I could reduce that to about ((1-.91)/(1-.78) = 40% of my current risk. Or reduce my odds from a 0.1% chance to a 0.04% chance. Of being hospitalized this year, for COVID.
Do I even need to start listing the diseases that I ought to be worrying about, more than that? Just to choose one, for men my age, that compares to an almost 2 percent annual risk of initial heart attack.
To sum it up, right now, my odds of being hospitalized for COVID-19 are slightly higher than my odds of being hospitalized for cholera. But not by a whole lot.
As a result, even though I believe that a second booster dose “works”, I just don’t see this as an opportune time to get it. Instead, I think I’ll keep my options open, and keep an eye on the new case rate in my area. If it looks like we’re heading into another wave, sure, I’ll get my second booster. Until then, I think I have better things to worry about.
