The headline to this post sounds absurd, I know, but for once this isn’t a case of the CDC not knowing what it’s doing or pushing a counterproductive message. The takes from scientists about the strange outbreak on the Yankees that I’ve read over the past few days have convinced me (and others) that it’s much ado about nothing, and may in fact be smoking-gun evidence of how effective the vaccines are.

But even so, I think the agency made a mistake bordering on irresponsibility in excitedly telling the country a month ago that there were only 5,800 breakthrough infections confirmed among more than 66 million people vaccinated at the time. It’s easy to understand why they were seduced into doing that: Such a tiny number of cases in such an enormous population was dramatic evidence of how shockingly well the vaccines work. But the logic was shaky. An average person who’s vaccinated and infected but asymptomatic would have no reason to seek out a COVID test, so the number of confirmed breakthrough infections doesn’t tell us much of anything about how many actual breakthrough infections there are out there. And by setting a baseline expectation that breakthrough infections are really, really, really rare, the CDC set itself up to be second-guessed whenever there’s an outbreak among vaccinated members of a sports team or a random vaccinated celebrity tests positive. “How rare can it be if people I’ve heard of are testing positive?” Americans are destined to wonder. “Maybe the vaccines aren’t as strong as the CDC thought.”

Instead of focusing on the not-very-useful number of confirmed breakthrough infections, the CDC should have said, “It doesn’t matter how many breakthrough infections there are. It matters how many vaccinated people are sick. Someone who tests positive but has no symptoms should be indifferent to the fact that they’re infected unless they’re around vulnerable people.” And in fact, the CDC is sort of saying that now by announcing that it won’t track all breakthrough infections going forward, only ones that result in severe cases.

If they had said that from the beginning — focus on illness, not on whether vaccinated people are testing positive — this Yankees thing would have been a nothingburger from the start.

Rochelle Walensky is now trying to convince people that the Yankees’ situation is basically good news, which it is. They’re up to nine people in the organization who are infected but so far only one has had symptoms and he was reportedly feeling better after a few days. The latest confirmed case, an unnamed staffer, was feeling good despite his diagnosis according to manager Aaron Boone. So what does that tell us?

Their mild or nonexistent symptoms showed the benefits of the vaccine, CDC Director Dr. Rochelle Walensky said on ABC’s “This Week” on Sunday.

“This is the vaccine working,” she said. “This means that you didn’t get infected, or you didn’t get a severe infection, you didn’t require hospitalization, you didn’t require death, and most likely those people were not transmitting to other people. So that is what we were working on the vaccine doing, we were hoping it would do.”

The threshold question is: “How unusual is it for an organization to have a rash of breakthrough infections?” When you hear a number like “5,800 out of 66 million,” you think of random fluky cases dispersed widely across the population, not a cluster of nine people. Per NPR, MLB conducted more than 10,000 tests over the past week and got only 10 positives — nearly all of which came from the Yankees. Weird! But another way to look at their outbreak in trying to gauge how effective the vaccines are is to try to guesstimate how many people would have been infected if not for the fact that more than 85 percent of the Yankees’ traveling staff are vaccinated. Two epidemiologists, Zach Binney and Angela Rasmussen, did some math:

Last July, 18 players and two coaches on the Miami Marlins tested positive. Shortly after, the St. Louis Cardinals saw its own outbreak among 18 people (10 players and eight staff). These would have represented at least 30 to 40 percent of a typical traveling party in 2020. In the National Football League, the Tennessee Titans had 24 cases (13 players, 11 staff) in October, while the Baltimore Ravens had more than 12 cases in December. These both represented about 20 percent of players; the percentages for staff are more difficult to estimate.

All of these outbreaks occurred under tighter covid-19 protocols than what the Yankees were under, including greatly limited shared indoor time and strict masking requirements. Vaccinated Yankees were allowed to spend unmasked time together indoors in hotels and clubhouses. Coaches and staff, who represent eight of the nine cases, were in tight indoor quarters during a rain delay just before the outbreak began. This is a perfect environment for the virus to spread, much like the Skagit County, Washington, choir practice outbreak in March 2020 that sickened about 86 percent of the 61 attendees.

Without vaccines, then, one could reasonably guess that at least 40 percent of the roughly 60-person Yankees traveling party, or 24 people, would have been infected.

If 24 people “should have” been infected but only nine were, then vaccination spared 63 percent of those 24 from infection — an efficacy rate right in line with the 66-72 percent efficacy rate of the Johnson & Johnson vaccine, which is what the Yankees organization used. So 15 people dodged infection after being vaxxed and eight of the nine who tested positive dodged symptoms, and the one who didn’t, 50-year-old coach Phil Nevin, apparently shook off his illness in a few days.

Seems like a good outcome.

In fact, one virologist told the Daily Beast that he’d consider Nevin the only true breakthrough infection out of the nine. If the other eight didn’t have symptoms then how, exactly, did the virus “break through”? All it did was sit in their throats long enough to show up on a PCR test. The only reason we know that nine staffers were infected is because MLB teams are testing everyone fanatically, three times per day, regardless of vaccination status. If those nine staffers were working average jobs and left to seek out their own COVID tests, probably the only breakthrough case who would have showed up in the data is Nevin, and that’s only if he took it upon himself to go get tested after experiencing symptoms. Maybe he would have told himself “I’ve been vaccinated for COVID so this must be the flu” and then forgotten all about it after he felt better in a few days.

The lingering mystery is how the Yankees ended up with a cluster, though. Did they fall victim to a variant, maybe? Some variants, like the South African strain, are better at punching through immunity than others. If the Yankees ran into a strain like that, the CDC should want to know about it immediately. The other unanswered question is just as important: Who infected whom, exactly? Did some unvaccinated person with a high viral load come into contact with the nine Yankees personnel and infect them all in a superspreader event, which is what most scientists assume? Or did Nevin or one of the other vaccinated staffers infect their colleagues? That would be newsy because vaccinated people are thought to infect others only very rarely. “It’s really hard to even sequence the virus [in vaccinated people] sometimes because there’s very little virus, and it’s there for a short period of time,” one virologist said to the Times. If Nevin infected the people around him, the CDC should want to know that too. Although, again, because none of his colleagues had symptoms, it would only prove the point that even vaccinated people with breakthrough infections aren’t a risk to others — at least if those others are vaccinated as well.