Post #1392: A funny thing happened on the way to COVID vaccine ineffectiveness …

Posted on January 10, 2022


The funny thing is that it’s not happening.  Not yet, anyway.

Here’s why I’m writing this.  Based on the research I looked at a couple of weeks ago, I thought that standard two-shot vaccination  did more-or-less nothing to prevent an Omicron infection.  (Ditto for prior COVID infection.)  And so, I’ve been checking the numbers on infections broken out by vaccination status.  I’ve been expecting to see infection rates level up, between the vaccinated and unvaccinated populations, under Omicron.

But that’s not happening.  At least, not yet.

As-observed, in the population, vaccinated individuals are still vastly less likely to get infected, get hospitalized, or die from COVID-19.   Even now.  Even with Omicron.

You might think, well, sure, that’s probably due to the high fraction of the vaccinated who have gotten a booster shot.  Boosters greatly increase vaccine effectiveness against Omicron.  And the “boostered” population is counted as part of the fully-vaccinated population.

But, in addition, the idea that two-shot vaccination is completely ineffective against Omicron appears to be wrong.  And since I’ve repeated that here, I need to say mea culpa.  That notion — that two-shot vaccination does nothing —  is based on test-tube studies of antibodies alone.  But antibodies are only part of the immune system.  Studies that look at people, instead of test-tubes, now appear to show that two-shot vaccination is 30% to 40% effective in preventing any symptomatic illness, and 70% effective in preventing hospitalization with Omicron.

As a result, this remains primarily a pandemic of the unvaccinated.  Even now.  Even under Omicron.

Now let me support those statements in red with a few bits of data.

Most recent estimates of vaccine effectiveness and Omicron.

Everybody seems to be in agreement that the existing COVID vaccines are less effective against Omicron than they were against Delta.  But …

But you have to realize that a) much of that evidence is from other countries, where the situation may differ, b) some of that is from test-tube studies of immune reactions, not actual counts of who did and didn’t get sick, and c) there’s a fair degree of uncertainty around all those estimate, and the numbers keep changing as more research comes in.

And, as importantly, what the research actually shows is not that vaccines don’t work against Omicron, but that immunity fades over time.  Whether or not your two-shot vaccine regimen provides you with any material protection against Omicron depends to a large degree on on how long ago you got your last shot.  If you’re fresh off your second shot, you’ve still got a pretty good level of immunity.

The upshot is that every time I look at this issue, the best estimates change. 

And so, if you thought — as I did — that two shots of vaccine did more-or-less nothing to stop you from getting an Omicron infection, well, that information is out-of-date.

For this, I’m just going to point you to (what I believe to be) a good, timely, and readable summary of the current evidence.  This is “By the Numbers: COVID-19 Vaccines and Omicron”, by Yasemin Nicola Sakay, date 1/7/2022, on Healthline.

Source:  Healthline, cited above.  Emphasis mine.

And, just to be completely clear, the headline you see below is not correct.  It’s an exaggeration.  It is true that the measured antibody response was basically zero.  But it’s not correct to infer that vaccines provide no protection.  There’s more to the immune system than just antibodies.

Source:  Harvard University, red lines are mine.

These test-tube studies are quick and cheap, and that’s why they are useful. Basically, you take blood from vaccinated individuals, toss in Omicron or a close substitute, and measure what happens as the antibodies in the blood react with the virus.  But such studies don’t (and can’t) provide an estimate of the overall immune system response generated against Omicron by vaccination.

There’s an important policy implication here.  People who claim that there is no need for further vaccination, because vaccines don’t work against Omicron, are simply wrong on the facts.  The vaccines don’t work as well against Omicron as they did against Delta.  But they still work to a material degree, particularly in terms of keeping you out of the hospital (and, by inference, dying from COVID-19).

Seems like forever since Omicron got here.

But it’s not.  I just need to document that Omicron was already widespread in the U.S. well before Christmas.  You need to know that, because most of the data on COVID infections by vaccination status date to that period.  The CDC now estimates that Omicron accounted for 77% of new cases for the week ending 12/25/2021.  It accounted for the majority of cases in almost every region of the country (purple segments below)

Source:  CDC COVID data tracker accessed 1/10/2022.

We still have large differences in infection rates between the vaccinated and unvaccinated populations.

Let me start with New York.  New York was hit hard and early by Omicron.  They also happen to tabulate their infections by vaccination status in exactly the format that I need for this exercise. So let me start with the New York State web page on breakthrough COVID-19 infections in adults.

Source:  the New York State web page on breakthrough COVID-19 infections in adults., accessed 1/10/2022.

In New York State, so far, there has been no material change in the observed effectiveness of vaccination (including boosters).  Contrast the vaccine effectiveness estimates in the Omicron era (circled in red) with those in the Delta era (circled in green).  They appear identical to within statistical error.

This doesn’t mean that vaccinated people aren’t getting infected with Omicron.  They are.  As the odds of infection have risen, they have risen for everybody.  But this means that relative odds of infection — between the vaccinated and unvaccinated populations — have remained the same.  Vaccines work, but they aren’t magic.

I can now take the share of the population that is fully vaccinated, and crudely estimate the approximate fraction of new cases and new hospitalizations that are due to the unvaccinated population.  (The “crude” part is that I’m lumping the partially-vaccinated in with the completely unvaccinated).  Currently, 83.9% of the New York adult population is fully vaccinated (Source).

The upshot is that the 16% of the New York population that is not fully vaccinated accounts for more than half of new COVID-19 infections, and almost two-thirds of new COVID-19 hospitalizations.  Even now — with only 16% of the population not fully vaccinated — the COVID-19 pandemic in New York is still mostly a pandemic of the unvaccinated.  Those not fully vaccinated still account for the majority of new COVID infections and hospitalizations.

Now let me repeat this calculation with data from Virginia, for roughly the same time period.  Virginia’s case rate data are for the entire population, so this shows vaccination rates for the entire population.  (That, in part, explains why Virginia’s rates are so much lower than New York.  This table includes children).

Source:  Vaccination data from CDC COVID data tracker.  Case rates from Virginia Department of Health.

Completely unvaccinated individuals account for just 20% of the Virginia population.  But they accounted for 69% of COVID infections, 78% of COVID hospitalizations, and 82% of COVID deaths.  In an era when the overwhelming majority of new cases were Omicron cases.

Let me now graph that the other way.  If we focus on the 69% of the population that is fully-vaccinated, the graph looks like this:

As we enter the fourth week of the Omicron wave in the U.S., and hospitals start filling up, let’s not fall victim to false equivalence regarding vaccination.  This is still — even under Omicron — mostly a pandemic of the unvaccinated.