Post #1273: Flu shot congestion and COVID-19 boosters.

Posted on October 1, 2021


If you got the Pfizer vaccine at least six months ago, and have some sort of risk factor (age, medical condition, high-exposure workplace, high-exposure residence), you are eligible to get a booster shot.

But if my experience yesterday was any example, be prepared to stand in line.

This post walks through the evidence around the need for a COVID-19 booster shot, and the rules for who does and does not qualify for one right now.

Every year, I get the flu shot at my local Safeway.  It’s not that I particularly enjoy the ambiance of health care in a grocery store.  It’s that a) they give me a coupon good for 10% off my next batch of groceries, and b) it’s never crowded.  I’m always the only person there getting a shot.

In a typical year,  that is.

Yesterday my wife and I went to that same Safeway — mid-day, mid-week — to get our flu shots.  It was crowded.   To a point that I’d never seen before, at that location.  They were overwhelmed with customers seeking vaccine shots.

I asked the pharmacist when would be a good time to come back for a COVID-19 booster, and she just laughed.  Of late, she’s been doing vaccinations all day, every day, and then doing her actual job (filling prescriptions) on OT.  She was cheerful about it, but it was clearly not her normal job.

At some point, we’ll go back for booster doses of the COVID-19 vaccine.  So the rest of this post is about the COVID-19 booster shots.  I found that a lot of the evidence and a lot of the rules were less than crystal-clear.  So I’m writing them up, to make sure I understand them.

COVID-19 booster doses:  The Evidence

Anyone who ever got a “tetanus booster” as a kid understands the notion of vaccine booster shots.  Some vaccines provide adequate immunity for life (e.g, MMR (measles) vaccine).  Others need to be renewed to maintain immunity.  Of which, arguably the “tetanus booster” is the one most of us would recognize.

My point is, vaccine boosters are nothing new.  Although, of course, in the nut-o-verse, the existence of a COVID-19 vaccine booster is being treated as some huge, unprecedented event.  By people who apparently cannot remember ever having gotten a tetanus booster shot as a kid.

This is different from the annual flu shot.  There, it isn’t so much that your immunity has faded, it’s that the disease you face changes every year.  The CDC picks the three strains they think will be most prevalent, and they have contractors create, in effect, a different flu vaccine every year.

In the case of COVID-19 vaccines, I had a few simple questions that I wanted straightforward answers to, regarding a COVID-19 booster shot.  And, for this, I’m turning to a document summarizing the evidence for the CDC advisory committee that made the decision to recommend booster shots late last month(.pdf).  Formally, the document is titled:  “Evidence to Recommendation Framework: Pfizer-BioNTech COVID-19 Booster Dose”, by Sara Oliver, MD, MSPH, ACIP Meeting, September 23, 2021.

Henceforth, Oliver 2021.

So this is straight from the horse’s Powerpoint.

Question 1:  Why only Pfizer?

Answer 1:  Because that’s the only one for which a booster has been tested, so far.

Are we seeing a booster recommendation for Pfizer, and not the other vaccines, because the others don’t need it?  Or is it merely because the others haven’t tested it?

The answer is that the others (Moderna, J and J/Jansen) haven’t been tested.  The only reason you see a booster shot recommendation for Pfizer (only) is that nobody has yet measured the impact of a booster shot for the other two.

The evidence suggests that immunity fades at roughly the same rate for all three vaccines.  That’s been measured as immunity against any infection, against symptomatic infection, and against infection that’s bad enough to get you hospitalized.  The “any infection” immunity fades fastest, the “hospitalization” immunity fades the least fast.  Here’s the chart for vaccine effectiveness against symptomatic infection, by time since vaccination.  The downward sloping red lines show that vaccine effectiveness declines over time.

Source:  Oliver 2021, page 16.

Above, the top row of boxes is Pfizer, the bottom row is Moderna.  I don’t see a lot of difference between those two rows.  The upshot is that there is more-or-less equal evidence of a need for a booster for both vaccines.

Question 2:  How well does the Pfizer booster work?

Answer 2:  It cuts your odds of infection or hospitalization by ~90 percent, relative to being vaccinated but skipping the booster.

There isn’t a whole lot of information on how effective the COVID-19 booster shots are.  So far, almost all the evidence on booster shots comes from Israel, and is “observational data” of various types.  That is, they looked back at cohorts of individuals who did and did not get a booster dose of the Pfizer vaccine.  That’s inherently less reliable than a clinical trial.  And, on top of that, they had very little time to assess effectiveness (very few days observed after the booster shot).

That said, across a handful of different studies, the booster shot seems to provide a massive increase in immunity, compared to vaccination without a booster shot.  (And recall that  vaccination without booster dose provides a massive increase in immunity over no vaccination at all).

Calculating from the various studies presented, getting the booster shot cuts your chance of infection or hospitalization by about 90 percent, relative to being vaccinated but skipping the booster dose.

But, you may say, so what?  Vaccination alone, without the booster, seems to provide pretty good protection already.  Are we just painting the lily here, trying to squeeze out a bit more protection from what is already a negligible risk of infection?

No.  The additional protection seems to be quite material.  At least to me.  They included a summary chart that makes that crystal clear.  This is a classic “number needed to treat”.  This shows how many people would need to get a booster shot, to avoid one hospitalization:

Source:  Oliver 2021, page 16.

To read this chart, if you are 65+, by getting the booster, you’ve avoided a roughly 1-in-500 risk of being hospitalized for COVID-19 in the next six months.  Similarly, if you are 50-64, you would avoid a roughly 1-in-2000 chance of COVID-19 hospitalization in the next six months.

From where I sit, that 1-in-500-ish benefit looks pretty substantial.  Particularly given that, in my age group, somewhere around half the people who walk into the hospital with COVID-19 never walk out of it.  So I’m seeing a fairly material benefit in avoiding that 1-in-500 over the next half-year.

But there are many ways one might look at this chart.  By far the simplest is strictly in terms of cost.  For which populations would the cost of the avoided hospitalizations more than cover the cost of the booster shots themselves?

Taking Medicare as a middle-of-the-road payer, as of March of 2021, Medicare pays $40 for administering the vaccine, and the Federal government paid Pfizer about $20 for the vaccine itself, for a total cost per booster of about $60.  I believe that the last time I looked at data from Medicare, the average cost per COVID-19 hospitalization was about $25,000.  That means that, over this six-month window, the booster pays for itself in hospitalizations alone if it takes less than (25,000 / 60 =) 413 shots to avoid one hospitalization.

Under that criterion, the booster shot does not quite pay for itself in avoided hospital costs alone.  It’s close, for the elderly.  But not for the remaining populations.

I will note, in passing, that if you look at that chart, you can easily see why the CDC might recommend boosters for some, and not for others.  At least at the moment.  It’s not as if they just made that up.  It’s that the benefit of the booster is much higher for the elderly and at-risk.  And that risks from the vaccine, such as they are, tend to be more evenly spread.  And the most common serious risk — myocarditis — is highly concentrated among young men.  I think you can plausibly see where CDC might urge the elderly to get a booster, but maybe not the young.

That said:

  • it works (it boosts your immunity to COVID-19)
  • it’s free (to the recipient)
  • it’s essentially risk-less — expect the same side-effects that you got from your second dose (except see below).

Looking at that chart above, my response is, why not?  For my part, I expect to see a COVID-19 winter wave that is at least as bad as last year.  Possibly worse, owing to our greatly reduced COVID-19 hygiene now, compared to last winter.  And, as I’ve said from the outset, your primary patriotic duty in this pandemic is not to be the next person filling a hospital bed.

One final aspect covered by Oliver 2021 is side-effects.  I read through it, starting on page 41.  My overall conclusion is that, in general:

  • Fewer side effects were reported with the third (booster) dose, though they suspect that was due to under-reporting.  (If you expect a side effect, based on your last shot, and you get that, presumably you are less likely to be upset about it.)
  • But, in one study, there seemed to be a much higher incidence of swollen lymph nodes for the booster shot (about 5% reported that) than for the original vaccination (about 0.4% reported that).

For those of you worried about what is arguably the worst known side effect — myocarditis — look at the chart provided on page 46.  There they estimate that the risk of myocarditis (24 per million doses, in males) with the booster (based on the original vaccination risk) is less than the risk of being hospitalized if you don’t get the booster.

So, for me, aside from that single caveat about lymph nodes, I’d judge that to say, more or less, it’s likely to be no worse than your last COVID-19 vaccination.

Booster dose rules in Virginia:  The Rules

Briefly, here are the rule for Virginia.  This is all from the Fairfax County Department of Health website, but I expect these are pretty much the same in all states.  The actual rules make a distinction between those who should get a booster, and those who may get a booster.  I don’t respect that there.  This is a list of anyone who currently qualifies for a COVID-19 vaccine booster shot.

Rule 1:  Pfizer only, at least six months after your last shot.

If you got either Moderna or J and J, then, in theory, you can’t get a booster.  And if your final vaccine shot was less than six months ago, ditto.  If you’re thinking about a booster, the first step is to pull out your vaccination record and check the date of your last shot.

Rule 2: 

  • 65 or over OR
  • 18 and over, and have at least one risk factor OR
  • 18 and over, and work in a high-risk setting OR
  • 18 and over, and live in a long-term care facility OR
  • 18 and over, and live in some other high-risk setting.

The list of risk factors (in Virginia, at least) is exactly the same list that was used to assign vaccination priority the first time around.  It is maintained by CDC and can be found at this link.  As before, this is an honor system.  If you say you have any one of these conditions, you qualify for a booster dose.

  • Cancer or history of cancer
  • Chronic kidney disease
  • Chronic lung diseases
  • Dementia
  • Diabetes (type 1 or type 2)
  • Down syndrome
  • Heart conditions (including high blood pressure)
  • HIV infection
  • Immunocompromised state
  • Liver disease
  • Overweight and obesity
  • Pregnancy
  • Sickle cell disease or thalassemia
  • Smoking, current or former
  • Solid organ or blood stem cell transplant
  • Stroke or cerebrovascular disease
  • Substance use disorders (e.g., alcoholism)

List of high-risk work settings is given on Fairfax County Department of Health website, but ultimately is determined by the US CDC.  Those occupations are:

  • First responders (healthcare workers, firefighters, police, congregate care staff)
  • Education staff (teachers, support staff, daycare workers)
  • Food and agriculture workers
  • Manufacturing workers
  • Corrections workers
  • U.S. Postal Service workers
  • Public transit workers
  • Grocery store workers

List of high-risk residential settings is less formalized, and is only given on the CDC website cited above.  The brief list is ” … reside in certain settings (e.g., health care, schools, correctional facilities, homeless shelters) …”.  I think they may be a little vague about that to avoid highlighting that, as with the original round of vaccines, prison inmates are eligible for booster shots before the general public.

Rule 3:  Bring your vaccination card.

If you’ve lost it, you can request a replacement here.  Apparently, they will check to see that a) you got the Pfizer vaccine and b) you last shot was at least six months ago.  Presumably, beyond your age (via driver’s license), everything else is on an honor system.

In Fairfax County, you can get a booster directly from the Department of Health, at one of two locations.  You can either schedule an appointment, or walk in.  Details of times and locations are in the FAQ section of this web page.

You can also get one at your local pharmacy, or possibly from your primary care physician.  You can check the list of providers at  There’s no lack of options in my area, and I suspect that’s true for most of the country.


Given that these only became available a few days ago, I suspect that most of the crush at my local Safeway was for COVID-19 boosters.  I’ll wait a while, and let the crush die down a bit.  (I have to wait a few days, in any case, as it hasn’t been quite six months since my last shot.)  And then I’ll stand in line and get my booster.

Just doing my part to keep this from happening in Virginia this winter:

Source:   CDC COVID data tracker.