Consider this a follow-up to last night’s post about the curious case of the Kentucky nursing home where most residents were fully vaccinated — and an outbreak of COVID happened anyway, thanks to a nasty little variant of the virus. With 40 percent of Americans having received their first dose and the country hopefully on its way to herd immunity, we’re faced with a new coronavirus mystery: What share of vaccinated people will suffer “breakthrough infections”?

Is it really .008 percent, as the initial CDC data indicated? Because there shouldn’t be outbreaks happening in any vaccinated population, even a population of elderly people, if it’s .008 percent.

What we do know, even if we don’t know the exact number, is that the percentage is very, very low. Low enough that our scaremongering, bad-news-obsessed media resorts to headlines like this to frame a story about a mere 71 out of 226,000 fully vaccinated people testing positive for COVID:

This is how @stltoday decided to play and headline a story that 0.03% of people who have been vaccinated in St. Louis County later tested positive, resulting in two hospitalizations and 0 deaths so far. pic.twitter.com/YRtTJlRR1m

— Brent Jones (@brentajones) April 20, 2021

“Vaccinated Test Positive” isn’t news given that we already know that the mRNA vaccines are “only” 95 percent effective. If anything, the news is that they seem to be more effective than one might expect from that 95 percent figure.

CDC director Rochelle Walensky went on the “Today” show this morning to try to calm people’s nerves about reports of “breakthrough infections.” Not only are they to be expected with any vaccine, she explained, but many vaccinated people who get infected aren’t experiencing symptoms and aren’t carrying enough of a viral load to get anyone else sick:

CDC Director Dr. Rochelle Walensky on rare cases of people who are fully vaccinated but still get COVID:
– 1/3 “are completely asymptomatic”
– Many “can’t transmit to others” pic.twitter.com/vlSbMk91ga

— The Recount (@therecount) April 22, 2021

Maybe that sales pitch will help reverse the downward national trend in vaccinations ever since the Johnson & Johnson vaccine was paused.

This summary by scientist Eric Topol is the best data I’ve seen yet on what rate of “breakthrough infections” vaccinated people might expect:

With addition of the new reports yesterday, the "breakthrough" infection rate after full mRNA vaccination has been consistently below 1%. Most are without symptoms, only detected by testing. Not included is the CDC report of 0.008% among 66 million people (no reference) pic.twitter.com/gJ4LJ3eAns

— Eric Topol (@EricTopol) April 22, 2021

In every case the rate was below one percent and, not surprisingly, it was highest among a cohort of elderly people, whose immune systems are weaker. The rate of symptomatic breakthrough infections is obviously smaller than the overall rate of infection in each case and the rate of hospitalizations among the vaccinated smaller still.

Even so, there must be some number of infections among those who’ve been immunized that scientists are missing. Per Slate:

For one thing, breakthrough cases can only happen when vaccinated people are exposed to COVID-19, and since most people were vaccinated recently, they haven’t had much time to be exposed. Another factor driving the number down may be that vaccinated people who have symptomatic breakthrough infections might not get tested because they assume they can’t be sick with COVID-19.

Right, it could be that some segment of vaccinated people are having mild symptoms for a few days reminiscent of the flu and assuming that it must be the actual flu rather than COVID, since they’ve been vaccinated for the latter. But in reality what they’re experiencing is a COVID breakthrough infection that’s been rendered mild by the antibodies in their system. If that’s the case then there are probably many, many more cases in which vaccinated people get infected, don’t have any symptoms, and never bother to get tested to confirm that they’re infected because, well, why would they? They feel fine and they’re operating on the false but understandable assumption that they can’t get infected because they’ve been vaccinated.

The real mystery in the post-vax stage of the pandemic, then, is how many vaccinated people are walking around who (a) are infected, (b) have no symptoms, and (c) have enough of a viral load to infect others. The problem of asymptomatic carriers unknowingly infecting others has been the curse of COVID from the start; it may be that mass vaccination will solve that problem almost entirely by preventing infection in ~99 percent of potential carriers who’ve been inoculated but not quite entirely. How many vaccinated but infectious people without symptoms will be out and about in red states this summer and fall, mixing with a large minority that refuses to be immunized and is still vulnerable?

I’ll leave you with this clip of Biden from yesterday warning that we need to keep up the pace on vaccinations in May and June if we want to be able to safely hold small gatherings on July 4. Um, Americans will be holding gatherings on July 4 no matter happens in the next two months, Joe. The vaccinated will do it because they’re safe and the unvaccinated will do it because they won’t care about the risk. Him saying this made me laugh the same way Scott Gottlieb did when he told CNBC this morning that, due to COVID’s seasonality, we’re not going to be having Christmas parties in restaurants this coming December. What he meant to say is that we shouldn’t be having those parties. But we will be.

Biden: "Back on March 11, I outlined a vision of what America could look like by the 4th of July. An America that was much closer to normal life that we left behind a year ago. We remain on track for that goal…[but if we] stop being vigilant, this virus will erase the progress" pic.twitter.com/7yofk9UUnl

— Aaron Rupar (@atrupar) April 21, 2021