Right now Jon Heyman’s the only reporter I’ve seen claiming that all five coaches were vaxxed, although ESPN has corroborated that five coaches tested positive. But Heyman’s a respected sports reporter and works for MLB Network, which is owned by Major League Baseball, so he has no incentive to spread rumors that might embarrass the sport. And, one would hope, he’d be extra confident in his reporting before making an explosive claim like this.

Because if it’s true, a lot of Americans are going to want the CDC to explain how five fully immunized people in close contact could all get infected given that the CDC’s best estimate of “breakthrough infections” is .008 percent and it’s widely assumed that vaccinated people rarely spread the virus to others.

Yankees have 5 coaches with Covid. All had been vaccinated, word is. Most asymptomatic. No players known to have Covid to this point. Game up in air tonight.

— Jon Heyman (@JonHeyman) May 11, 2021

The Yankees are only confirming one positive test:

#Yankees statement: “We have a breakthrough positive involving 3B Coach Phil Nevin, who is fully vaccinated. He's currently under quarantine protocol in Tampa. Under MLB’s guidance and advice, and with its assistance, additional testing and contact tracing are ongoing.”

— Joel Sherman (@Joelsherman1) May 11, 2021

Boone said at this point Nevin is the only coach who has tested positive, but others are in contact tracing. Said no players impacted and game will be played tonight #Rays #Yankees

— Joel Sherman (@Joelsherman1) May 11, 2021

Did Heyman get his wires crossed maybe, confusing the fact that other coaches are quarantining as a precaution with positive test results? Or is there really an outbreak among a group of vaccinated people?

If there is, it wouldn’t be the first time we’ve heard of one. Remember that a study of an outbreak at a Kentucky nursing home found 18 out of 75 vaccinated residents got infected thanks to a nasty variant. One died. But that outbreak could be understood as something of a worst-case scenario — senior citizens with weaker immune systems clustered together in close quarters and exposed to a tricky strain of the virus. And even so, most who were vaxxed dodged infection.

An outbreak on the Yankees coaching staff would be harder to explain. Although if it turns out Nevin and the others had no symptoms, the CDC will presumably shrug it off and say, “No harm, no foul.”

As I’m writing this, Heyman has posted an update that seems to be backing off his initial report. If it turns out he was wrong earlier, he’ll never hear the end of it. And he’ll deserve not to:

To clarify: Only 1 Yankees coach is confirmed positive. Others are being tested/retested.

— Jon Heyman (@JonHeyman) May 11, 2021

It’s probably the case that many more vaccinated people than we think are getting infected but they never know it because they’re asymptomatic and thus have no reason to get tested. Sports teams are different because they get tested routinely; MLB is requiring players and coaches to get swabbed every other day. It stands to reason that we’d detect more “breakthrough infections” in a group like that, where even people with no symptoms are tested repeatedly, multiple times per week.

Which means, if Heyman’s report bears out, the CDC may conclude from this that vaccinated people remain at very little risk of illness themselves but pose a greater risk than we thought of infecting others. So they’re going to want even vaxxed people to wear masks and take precautions unless they’re in an environment in which they know for sure that there are no unvaccinated people around. Sigh.

The good news is that the data supporting the benefits of vaccination continues to pile up involving samples much, much bigger than the Yankees coaching staff. For instance:

The Cleveland Clinic on Tuesday released a study showing that 99.75% of patients hospitalized with COVID-19 between Jan. 1 and April 13 were not fully vaccinated, according to data provided to Axios…

Details: The study also looked at 47,000 Cleveland Clinic employees who had received one shot, both shots or no shots at all.

The Cleveland Clinic found that 99.7% of its employees who were infected with the coronavirus were not vaccinated, and 0.3% of infections occurred in those who were fully vaccinated.

Whatever happens with Nevin, he’s unlikely to need hospital care. Hospitalizations are also heading downward in New York City as vaccinations continue to ramp up:

COVID cases have fallen by ~80% in the past 5 or 6 weeks in New York City, according to both state and city data. Starting to look a lot like Israel.https://t.co/FzTtPAVIGR pic.twitter.com/kglY1X0sTy

— Nate Silver (@NateSilver538) May 11, 2021

Here’s what Silver means by “look a lot like Israel”:

They’re down to a daily average there of 48 cases per day, the first time they’ve been under 50 since May 30, 2020. Almost a full year.

There’s no doubt that the vaccines work but I think there’s also little doubt that more vaccinated people than we know are walking around with asymptomatic infections and never have occasion to get tested before they clear the virus from their systems. The important question for scientists is how contagious those people are when they’re infected but asymptomatic. If the vaccinated are still capable of spreading the virus, the unvaccinated are at greater risk going forward than we may have assumed.