May 25th, 2021

Yes, the Yankees Had a COVID-19 Outbreak Even Though They’re Vaccinated — Here’s Why

John Clarkson, Boston Beaneaters, 1887. Library of Congress.

Hey Paul, aren’t you going to write something about the Yankees and their COVID-19 outbreak? How did this happen, aren’t they vaccinated?

So asked several of my friends, family members, and colleagues — understandably. I’ve never been shy about my unabashed obsession with baseball, nor my lifelong fandom of this particular much-reviled professional team, though it does earn me some good-natured ribbing here in Boston.

(I came to it honestly, having grown up in New York. And for the record, they were horrible the year I started rooting for them — 9th place. Yes I’m old, and yes that was quite the Impossible Dream year for the Red Sox.)

So here’s what happened with the COVID-19 outbreak among the Yankees, in as few words as possible:  Nine people tested positive (mostly coaches and staff, one player). One symptomatic, with mild illness. All vaccinated, all with the J&J vaccine.

How could this occur? After all, with the vaccines so effective, to have nine breakthrough cases seems downright freaky, a bioterrorism plot hatched by Red Sox fans. Or if not that, an act of divine retribution for years of being America’s Most Hated Team.

With the caveat that I don’t have any inside baseball knowledge (you got that joke, right?), here’s how this could happen:

  • The source of infection was a highly contagious person. The outbreak likely followed the over-dispersion model of SARS-CoV-2 spread, meaning one person spread to several others, rather than multiple different transmissions — a “super spreader” event, only with everyone vaccinated. This most likely happened indoors, and could have been introduced to the team originally from someone not vaccinated — but we don’t know that.
  • A more transmissible or resistant variant likely caused the outbreak. Though the J&J vaccine did reasonably well in preventing infection in regions with circulating variants, there was some decline in efficacy in South Africa and South America. While I hope someone is sequencing these cases, sometimes the amount of virus in vaccinated people who test positive is so low (especially in those who are asymptomatic) that sequencing fails.
  • The vaccine storage, cold-chain, and lot numbers need to be checked. Sometimes errors in vaccine handling happen that make it less effective. As if we needed a reminder that we’re still in unusual times, remember that baseball teams normally aren’t in the business of giving vaccines — they could have made a mistake.
  • The vaccine isn’t 100% effective. This is the J&J vaccine, remember — 60-70% effective in preventing symptomatic disease. And even the mRNA vaccines aren’t 100% effective, as shown by this nursing home outbreak. But they sure do prevent serious outcomes!
  • Most of these cases wouldn’t have been detected in the “real world” at all. Testing strategies in professional sports and the entertainment industry are intense, a far cry from what we do in the community. They test like crazy, especially once a case occurs, and generally have been using PCR — which picks up even fragments of viral RNA.

This last testing point deserves emphasis, because with all that swabbing and saliva collection — one report cited three times a day! — there’s a decent chance this kind of “outbreak” happens frequently all around us, but we just don’t know about it.

Regardless, the vaccine and the testing program did what it was supposed to do, meaning prevented severe disease, detected cases early, and prevented broad spread within the team. Most of the media coverage of the outbreak mentioned this favorable outcome.

Here’s a nice example, with an appropriate metaphor:

Cases that would have been hospitalizations become colds, and symptomatic cases become asymptomatic. Most infections are avoided entirely. The vaccine works like a strong head wind from the outfield, turning homers into doubles and doubles into harmless fly outs.

Love that!

And if the Yankees have any needs for an ID doc … my baseball achievements may have ended on my high school team, but I know an awful lot about antibiotics.

10 Responses to “Yes, the Yankees Had a COVID-19 Outbreak Even Though They’re Vaccinated — Here’s Why”

  1. Richard Iseke says:

    Great information. You are a voice of rational thinking in a world that needs it.

  2. Babu Bangaru says:

    lot of postulates/possibilities.
    Appreciate any follow up facts that may become available.

  3. Stefani Wedl says:

    This post made my day! As a physician and avid (SF Giants) baseball fan, thank you for breaking it down in an easy to understand and entertaining way.

  4. Katy Bowman says:

    Love that final offer to be the official Yankees ID doc. I can vouch they couldn’t pick anyone better!

  5. Diana Christensen says:

    Love it ! I am an ID physician, so well written!

  6. HealthTimes says:

    Great read, great article. Thanks for sharing information about this pandemic.

  7. Jon Blum says:

    One other point is that the more people vaccinated, the fewer cases – but the higher the percentage of those cases that will be in people who are vaccinated. If you have dealt with a measles or mumps outbreak, where most of the population is vaccinated, you have probably noticed this. This is shown graphically here:

  8. Babak says:

    Least possible but still one of possibilities is a cross-contamination error in PCR testing. One estimate shows the rate of operational false-positive covid swab tests could be somewhere between 0·8% and 4·0% (

  9. Souleymane TASSEMBEDO says:

    This remind us to be careful when talking about the COVID 19 vaccine particularly its efficacy.

  10. B. Accousti says:

    Hmmm Interesting. Still not convincing me of the wonders of that vaccine. Sorry

HIV Information: Author Paul Sax, M.D.

Paul E. Sax, MD

Contributing Editor

NEJM Journal Watch
Infectious Diseases

Biography | Disclosures | Summaries

Learn more about HIV and ID Observations.