What happened with that Yankees COVID-19 outbreak? What does it mean for vaccine effectiveness?

Testing and Contact Tracing Vaccines

A: While several vaccinated players tested positive, they were almost all asymptomatic.

TL; DR- Nine members of the New York Yankees tested positive for COVID-19 after receiving the Johnson & Johnson vaccine. Among those who tested positive only one reported mild symptoms. These cases were discovered because the Yankees test regularly, unlike most other vaccinated people. There were no cases of severe COVID-19. This is a good sign that the vaccine is working!

What does the Yankee’s outbreak tell us about testing and vaccine effectiveness?

➡️ TESTING: There is an old adage if you go looking for something you are more likely to find it. By continuing to regularly test people who are fully vaccinated, it is more likely you will find asymptomatic infection. Certain COVID-19 tests are very sensitive, especially PCR tests. These tests are made to detect even low levels of viral RNA. However, a positive PCR result does not necessarily mean that a person is going to get sick or can transmit the virus. In the case of the Yankees, players and staff were getting tested regularly and the Yankees further increased their testing after the first positive case was identified. It is not surprising that asymptomatic infections were discovered—this is to be expected. There are likely additional undetected asymptomatic infections among vaccinated people who never get tested.

➡️ VACCINE EFFICACY: The Yankees team members who tested positive had all received the Johnson & Johnson vaccine. In the phase 3 trial one shot of J&J reduced cases of symptomatic COVID-19 by 72% in the US, with no hospitalizations or deaths in the vaccine group. Reports say that close to sixty team members were exposed, but a smaller number tested positive. This number of positive cases is consistent with what is expected for J&J’s reported vaccine efficacy. So even though there were vaccinated individuals who tested positive for COVID-19, we should not be alarmed. With almost all asymptomatic cases and no severe disease or death, the vaccine is still working as designed.

🙋‍♀‍ What about transmission among the vaccinated?

One important question is whether vaccinated players passed on the virus to others. We still do not know how the team members were infected (there is an ongoing epidemiologic investigation). One possibility is that an unvaccinated person infected all of the players. The other possibility is that one or more vaccinated players transmitted the virus to the others.

Most scientists believe that vaccines will reduce risk of transmission by simply giving the virus less opportunity to replicate before it is neutralized by antibodies. Unfortunately, the trials did not test this directly, but real-world evidence is accruing that this is true (recent summary here).

One study showed that vaccinated people testing positive had lower viral loads than unvaccinated people testing positive, suggesting they may be less infectious. Nonetheless, this cluster of positive cases suggests it’s still possible for transmission to occur among vaccinated individuals. We’ll keep you posted on the outcome of the outbreak investigation which should shed more light.

➡️ BOTTOM LINE: Vaccines are highly effective at preventing serious disease and death. They also are likely to greatly reduce transmission, but not 100%. This is one reason why vaccinated people should still take precautions around unvaccinated and vulnerable people.

Those Nerdy Girls

Further Reading:

New York Magazine

The Washington Post

Stat News

Study on viral load

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