An uncharacteristically simple rule from the agency: If you’ve had the first two shots, you’re up to date if you’re not yet eligible for the booster and not up to date if you are.

But what about those of us who may have gotten, say, seven shots out of an abundance of caution? Which category is that?

Hypothetically speaking, of course.

Biden’s CDC Director says the definition of fully vaccinated is being changed to include the booster, and “fully vaccinated” will now be called “up to date.”pic.twitter.com/WgLKU80Gms

— RNC Research (@RNCResearch) January 21, 2022

Does this semantic nonsense achieve anything meaningful? They could have just kept “fully vaccinated” and applied the same definition as above, that you’re not fully vaxxed unless you’ve received every dose you’re eligible for. Given a choice between two bad options, confusing people with the “up to date” switcheroo or pissing them off by moving the goalposts on “fully vaccinated” status, it appears the CDC decided confusion was the lesser evil.

Imagine people who’ve had two doses presenting their proof of vaccination in vaccine-passport jurisdictions and finding out they missed the cut. “But I’m fully vaccinated!” “Maybe so, pal. But you’re not up to date.”

If you want to know why the CDC is making this change today, the answer probably lies in the fact that they just got the data from two new studies confirming that boosters provide a stellar defense against serious illness and want to call the public’s attention to them. Against Delta, a third dose provided 94 percent protection against trips to the ER or hospitalization. Against Omicron, it did nearly as well:

NEW: Today's @CDCMMWR study found that during periods of both #DeltaVariant and #OmicronVariant, a 3rd dose was highly effective at preventing #COVID19 associated emergency department visits, urgent care visits & hospitalizations. https://t.co/X8chSXviW7 pic.twitter.com/OMtvSgZU1J

— Rochelle Walensky, MD, MPH (@CDCDirector) January 21, 2022

That adds to a body of studies all showing strong immunity from severe illness for those who are fully “up to date”:

Now there are 3 reports for vaccine effectiveness vs Omicron hospitalization, @UKHSA, @KPSCalResearch and today's @CDCMMWR. They are quite consistent for marked protection of the 3rd shot (booster). My summary table here pic.twitter.com/2hE0jH8fO5

— Eric Topol (@EricTopol) January 21, 2022

A separate study found that people who were boosted had five times as much protection against *infection* by Omicron than the unvaccinated did, making the third dose especially important for those who live with vulnerable people:

Another @CDCMMWR study out today found that when the #OmicronVariant was first circulating in the United States, adults who got a #COVID19 booster dose had 5x the protection against infection compared with adults who were not vaccinated. https://t.co/EXj2fbrpBM pic.twitter.com/pXPAGMQino

— Rochelle Walensky, MD, MPH (@CDCDirector) January 21, 2022

The semantic switcheroo is obviously aimed at pressuring people who are eligible for the booster but haven’t received one yet to get down to business. Less than 40 percent of the vaccinated population has received a third dose, per WaPo; among senior citizens, the most vulnerable cohort, a third are still unboosted despite the fact that the CDC’s new dats shows unvaccinated people over the age of 50 were 45 times more likely to need hospital care for COVID than the boosted are.

All in all, America’s poor numbers on third doses helps explain why our Omicron wave is worse than the UK’s:

See below, yeah. Many people seem to think UK, among other examples, is doing as badly as the United States.

They have much better vaccination rates than the US, and also ahead on boosters… And it shows.

The United States is… almost a class of its own. https://t.co/SOMGZRJgtK

— zeynep tufekci (@zeynep) January 16, 2022

Our Delta wave was also worse than the UK’s even though another new study shows that natural immunity provides better protection against Delta than vaccination does. I’ve assumed all along that our rate of natural immunity and the UK’s rate have been comparable throughout the pandemic. Maybe that’s wrong?

For the study, health officials in California and New York gathered data from May through November, which included the period when the Delta variant was dominant.

It showed that people who survived a previous infection had lower rates of COVID-19 than people who were vaccinated alone.

That represented a change from the period when the Alpha variant was dominant, Silk told the briefing.

“Before the Delta variant, COVID-19 vaccination resulted in better protection against a subsequent infection than surviving a previous infection,” he said.

The best protection against Delta according to the study was natural immunity plus vaccination followed by natural immunity alone and then vaccination alone. Those with no form of immunity fared worst of all.

Maybe it’s not a matter of the UK having had much more natural immunity than we did but a greater share of fully vaccinated people. (Sorry, I mean “up to date.”) We led them in that metric until July 1, when they took the lead and never looked back. Within a month they were almost six percentage points ahead, which may have helped blunt Delta over there. As for boosters per 100 people, it’s no contest:

Despite the CDC’s push to get people boosted, SCOTUS’s ruling against Biden’s vaccine mandate is operating as a green light for some businesses to drop their own private vaccine mandates, slowing the uptake of third doses at the margins. It could be a long winter.

I’ll leave you with this. The CDC has lost a lot of public trust since the start of the pandemic. But it’s still the most trusted authority of anyone listed in this poll.

Net approval for the CDC’s handling of the coronavirus fell to an all-time low: 53% of voters approve of the CDC’s handling. https://t.co/dI3b5lmBLB pic.twitter.com/blgBZkMvi1

— Morning Consult (@MorningConsult) January 21, 2022