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Eight members of the New York Yankees organization who were fully vaccinated against Covid-19 tested positive for the coronavirus this week. And that news has led to a lot of people saying, wait, what?

Below, STAT outlines what we know about the cases and some of the factors that might have contributed to the cluster.

What do we know so far? 


On Sunday, third base coach Phil Nevin reported feeling some symptoms and tested positive for Covid-19. (He had recovered as of Thursday, General Manager Brian Cashman said.)

The team quarantined people who’d had close contact with Nevin and expanded its testing program, which turned up another seven asymptomatic cases by Thursday, when shortstop Gleyber Torres became the eighth person — and first player (the other seven were coaches and support staff) — to test positive.


All eight people had received the Johnson & Johnson Covid-19 vaccine and were considered fully vaccinated.

What does this mean about breakthrough infections and vaccines?

The Covid-19 vaccines have been shown to be overall highly effective at preventing illness, and even more so at staving off the worst outcomes, like serious disease and death. But even the best vaccines can’t block all infections, and those that still occur after immunization are called breakthroughs.

The clinical trials that led to the authorization of the different Covid-19 vaccines generally measured how effective they were at preventing symptomatic cases, and in its trial, the one-dose J&J shot proved to be 66% efficacious at blocking moderate and severe Covid-19. And while studies have shown the vaccines also prevent asymptomatic infections in many cases, researchers don’t have firm conclusions at just how effectively they do so. The assumption is that many asymptomatic cases go unreported in the absence of broad and frequent testing.

Which brings us to the Yankees. Eight breakthrough infections seem like a lot, and something odd could be at play here. But it’s notable that only Nevin had some symptoms. It’s possible that at least some, if not all, of the other seven other infections would have been missed if they didn’t occur on a team that’s undergoing regular testing.

And while it can’t be known for sure, it’s possible that without vaccines, this cluster could have been worse, both in terms of the number of infections and how sick certain people got. The Yankees travel with some 50 people.

Overall, the Centers for Disease Control and Prevention has received reports of 9,245 breakthrough cases, a tiny fraction of which resulted in hospitalization or death. More than 118 million people in the United States have been fully vaccinated. The low number of breakthrough infections has been touted as a testament to the power of vaccines, which are providing both protection for individuals and helping drive down transmission.

But experts also point out two caveats with the number of breakthrough infections. For one, some large number of the people who’ve been fully vaccinated haven’t since been exposed to the coronavirus, so it’s not known how many infections there would have been without that vaccine coverage. The tally of breakthroughs is also certainly an undercount because many asymptomatic cases go undetected — unless, of course, they occur in a setting with widespread and frequent testing, like on a professional sports team.

Two extra points: Starting Friday, the CDC will only report breakthrough infections that lead to hospitalization or death because those have the “greatest clinical and public health importance.” The Yankees cases, of course, didn’t rise to that level.

And Torres, the shortstop, had Covid-19 last year, indicating that his case is both a breakthrough infection and a reinfection. Scientists think reinfections remain rare, though given that second infections are generally thought to be mild or asymptomatic (akin to breakthrough infections), experts similarly don’t have great estimates for how often they occur. But considering Torres was asymptomatic, his case fit with what experts expect from most reinfections.

How did this happen?

The team has said it’s conducting contact tracing, and officials from both the New York state health department and CDC are in touch with the team. So far, it’s not clear how this transmission occurred.

Two of the most pressing questions we can think of:

Where did the spread initiate?

Essentially, was this a superspreading event during which someone — likely an unvaccinated person — passed the virus to the eight people? That is one probable explanation. The SARS-CoV-2 coronavirus is particularly adept at transmitting in crowded, indoor settings, so perhaps someone who was shedding lots of virus came into contact with the team, and that’s how this outbreak occurred. The Yankees have surpassed the threshold of 85% players and personnel vaccinated that allowed them under league and union rules to relax some distancing and masking requirements.

It’s also possible that some of the transmission occurred among the eight people who’ve tested positive, though that would seem to be a rarer event. Even if a vaccinated person contracts the coronavirus, it seems they’re generally less infectious to others than an unvaccinated person with Covid-19 — especially if they’re asymptomatic. That might be because the vaccine reduces the amount of virus these people can shed, and also shrinks the window during which they’re contagious.

Was there a variant involved?

Certain coronavirus variants — most notably B.1.351, which first emerged in South Africa but has circulated at low levels in the United States — cause breakthrough infections at higher rates than other forms of the pathogen. The vaccines still prevent many cases, and retain their overall protection against severe illness and death. But the shots do seem to lose some of their potency in staving off mild or asymptomatic infections, and may not be as powerful at preventing people who have breakthrough infections from passing on the virus.

Major League Baseball is working with a Salt Lake City lab for its testing and sequencing efforts, so we could eventually get more information about this question. The sequencing data could also provide insights into whether the eight people were infected during the same event or independently of each other.

Does this mean the CDC was shortsighted in its recommendation Thursday that fully vaccinated people don’t have to wear masks in most settings?

Depending on the type of mask, face coverings have generally been more about protecting others than yourselves, meaning they’re more of a tool to stop you from spewing virus out into the world than blocking virus headed your way.

There was also some nuance in the CDC’s updated recommendations. The data indicate that the chances of an asymptomatically infected person who’s been vaccinated spreading the virus are extremely low. But CDC Director Rochelle Walensky noted Thursday that if someone starts feeling sick, they should start wearing a mask again and get tested.

Still, critics of the CDC decision could point to the Yankees cluster as a sign that prudence is merited. While many experts celebrated the CDC announcement, others argued that the agency was premature or that it should have tied the guidance to hitting thresholds like a further reduction in new cases per capita or reaching a certain level of vaccination coverage. (Given the variability of infection and vaccination rates around the country, some places have achieved these milestones.) The concern is that with transmission still at the rate it is, and with vaccination rates as low as they still are, people who are unvaccinated or who haven’t mounted a strong immune response to vaccines (like some people with cancer are experiencing) will be more vulnerable to contracting the coronavirus than if the CDC had just waited a few more weeks.

Was this a fluke?

Not every member of the Yankees organization who tested positive this week was vaccinated at the same time, so the outbreak can’t be attributed to one bad batch of vaccine or an error in keeping the shots at the proper temperature. Still, in a pandemic in which hundreds of millions of people have been infected and amid a global vaccine campaign, there are going to be some weird outlier situations. Simply put, perhaps something bizarre happened with the Yankees.

It underscores how important it is to avoid drawing conclusions from one case involving fewer than a dozen people. The clinical trials that established the vaccines’ efficacy involved tens of thousands of people, and real-world data that have backed up what the clinical trials concluded: the vaccines are immensely powerful against Covid-19. 

  • None of these ads for vaccination address the significant segment of the population that possesses either natural immunity or acquired immunity via prior infection to the original virus and its current variants. As others have commented here, the focus should now shift to testing for relative strength of antibodies and the development of therapeutics.

  • Vaccination works – to prevent vaccinated people from getting sick. It does not stop infections, and can’t. Lots of people catch other coronavirus infections that cause colds, and flu infections as well without getting sick – but nobody is testing for these. These 8 baseball players were not sick, and only one had any symptoms at all. Baseball needs to stop testing. Just make sure all the players are vaccinated, and get rid of the tests already.

  • What nauseating over-hyping of break-throughs in this thrill-seeking rubbish article. It is this simple: JNJ vaccine is 72% effective against the Wuhan original, and only 52% effective against the South-African variant. Those percentages are from when people were wearing masks etc, so in reality they are likely lower. And it means that the other percentages still get sick. Those with immunity can always still be Covid carriers / spreaders – they just won’t get very sick (or die) themselves (that’s why everyone ought to get vaccinated). Immunity seems to also wane over time (hints towards future booster shots). All this has been very well known for quite a while. Due to their sharing and big-crowd life-style trying to find the source with the Yankees so late is ludicrous. This article is totally missing THE essential denominator : Testing For Antibodies. Replace the TA in STAT with HI – that is my judgement on this article.

  • Thanks for this article. What makes me wonder if the Yankees have been spreading the virus among themselves (infecting each other) is that they did not all test positive at the same time. Indeed since you wrote this article, another one of them has tested positive. Even taking into account that people’s immune responses might differ, doesn’t the time elapsed between case #1 and case #9 suggest they were not infected at the same time/by the same unvaccinated source? The fact that vaccinees don’t shed as much virus – or for as long a period – certainly suggests they’d be less likely to infect others, but do we really have enough data to conclude they can’t transmit? If not, seems like the vaccinated should stay masked to protect the unvaccinated – till more people are vaxed/case numbers are negligible.

  • I could tell by your comments who you voted for or otherwise support. People who would have at 1 time been called journalists should be noted for who they work for and who owns that organization. They have no scruples.

  • As a Yankees fan I am writing in the Interest of Full disclosure. It should be pointed out Stat is owned by the Boston Globe which is owned by John Henry. The Same John Henry who owns the Boston Red Sox; our arch rivals. This should have been acknowledge at the beginning of the piece so that readers could be made aware of any potential biases that the publication may have had.

  • Nothing blizzardy here. Most likely a variant for which the Jensen vaccine is weak, likely P.1-related or the British variant –seems a bit too soon for B.1.617.

    The breakthroughs, their count an important data point regardless of hospitalization (outside of politics unclear why the CDC would not publish it), suggest that gene sequencing should have been carried out. Especially because infections in a group w/ an 85% immunity further sheds worries about whether “herd immunity” will ever be possible.

    These cases are not a fluke, but a harbinger of things that might come and an opportunity to learn which seems wasted…

  • This thing is here to stay, get used to it people. Vaccinated or not, you WILL get this thing at some point. Let’s just move on, focus on early treatments and stop segregating people based on their health choices.

    • I agree with you. We will not be able to vaccinate our way out of this. Emphasis should have and still should be on therapeutics. Of note Pfizer has 2 in the works right now. The CDC is further compromising its integrity with pronouncements meant to encourage more people to vaccinate and not based upon data. The science people quote supporting the CDC decisions is marginal at best. The CDC decision not to look at all breakthrough infections looks like a misrepresentation, bias and manipulation of data. I hope their decision is based on being overwhelmed and understaffed because that is fixable where politicization is not.
      Hunker down folks, because we are not done yet.

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