Yankees “outbreak”

ST PETERSBURG, FLORIDA - MAY 13: Manager Aaron Boone of the New York Yankees looks on during batting practice before a game against the Tampa Bay Rays at Tropicana Field on May 13, 2021 in St Petersburg, Florida. (Photo by Julio Aguilar/Getty Images)

In one week, there were 9 cases of COVID-19 in fully vaccinated (Johnson and Johnson) members of Yankees baseball organization: 1 player, 3 coaches and 5 staff. This has led to confusion and questions about vaccine effectiveness in the general public.

Breakthrough cases are expected.

Vaccine efficacy is amazingly high, but not 100%. “Real world” efficacy of J&J is 72% (against old variants). In other words, if 100 people got COVID19, J&J could have prevented 72 of them. 28 people would still get some form of the disease, albeit, more mild. And this is what we saw with the Yankee “outbreak”. 8 of the 9 people were asymptomatic. 1 had mild symptoms. If these 9 players didn’t have the vaccine, they may have had severe disease.

With that said, we have to be careful how we label “breakthrough cases”. While, technically, an asymptomatic infection is considered a breakthrough case according to the CDC, we need to stop thinking like this. A breakthrough case is better defined if someone is vaccinated and gets the disease. COVID19 is here to stay and we (the public, the media, CDC) need to distinguish meaningful breakthrough cases from not meaningful ones. This will help us better understand variants, real world efficacy, and risk/reward balance for those that don’t have the vaccine yet.

Surveillance testing

The Yankee “outbreak” was discovered because Major League Baseball (MLB) tests often. During that week, MLB ran 10,629 tests, of which only 10 were positive (majority were Yankee’s). At this testing rate, you’re going to find exposures and infections. That’s the entire point of surveillance testing.

This is especially true because the MLB uses PCR tests. PCR tests are highly sensitive. In other words it can detect 10 particles (not 10 billion, not 10 million, but 10 individual particles) of the virus. This level of sensitivity is very useful during a global pandemic where the risk of disease, hospitalization, and death are a bit random. We needed to stop transmission at every corner. However, now that we are systematically testing among vaccinated, many scientists are advocating that it’s time to move from PCR to antigen testing.


Given 9 people (out of 60 on the traveling team) tested positive, this means that the vaccine does not stop transmission. But we knew this. Vaccines do not provide sterilizing immunity. Sterilizing immunity is the kind of immunity where, if you get exposed and the virus lands in your nose, it will be neutralized (or killed) immediately. It will not have a chance to replicate. This does not happen with the COVID19 vaccines. We know our COVID19 vaccines reduce viral load by about 70-95%. This means that a vaccine limits virus growth enough where it limits transmission. This does not mean it eliminates transmission.

This “outbreak” was also in part because of relaxed mitigation measures. The MLB implemented a pretty brilliant policy to encourage vaccines: Once a team is 85% vaccinated, all players/staff can…

  • Drop masks

  • Drop electronic tracing

  • Can carpool or use Uber or Lyft

Also, if this threshold is met, all vaccinated players/staff can…

  • Eat and drink on flights

  • Gather in indoor spaces such as hotels without masks or social distancing as long as non-vaccinated people aren’t present

  • Have close contact with someone with COVID-19 would not have to quarantine unless they exhibit symptoms.

  • Have the option to reduce PCR saliva testing to twice weekly

Also, if this threshold is met, family members who are fully vaccinated and children who are not vaccinated can

  • Stay with players and staff in hotel rooms during road trips

  • Sit anywhere in ballparks and not be restricted to pods, subject to local laws and policies.

The Yankees organization is one of the few teams that have met this threshold. So, masks and social distancing were relaxed before this “outbreak”. This allowed the virus to spread. Especially among the 60 traveling team/staff that were in close quarters for long period of time. Once the Yankees discovered this, they reimplemented public health measures until the virus calmed down a bit.

Bottom line. The Yankee “outbreak” is another example of the vaccine working beautifully. And this isn’t an outbreak. There was no disease associated with the vast majority of cases.

Love, YLE

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