I read on https://www.usnews.com/news/health-news/articles/2021-07-01/reports-of-some-getting-pfizer-moderna-boosters-after-j-j-vaccine-prompts-calls-for-more-guidance (mirror):

With the delta variant poised to become the dominant strain in the U.S., some Johnson & Johnson recipients are taking an additional shot from Pfizer or Moderna in the hopes of boosting their protection.

Are there any downsides in getting vaccinated with the Pfizer or Moderna COVID vaccines after having received the Johnson & Johnson's Janssen COVID-19 Vaccine, aside from the potential Pfizer/Moderna COVID vaccine side effects and using vaccine doses that could be better used on unvaccined individuals?

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    The article you link makes it clear there is no data on this. What data-based answer do you think answerers at StackExchange can provide that the CDC and FDA can't?
    – Bryan Krause
    Jul 25, 2021 at 22:01
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    @BryanKrause An answer based on the ~10k new research articles published since the article I link was published. Jul 25, 2021 at 22:24

1 Answer 1


No downside known so far. Getting a booster shot after having received the Johnson & Johnson's Janssen COVID-19 Vaccine has been more thoroughly studied, as summarized in https://abcnews.go.com/US/jj-vaccine-doses-start-fauci/story?id=80620642

The data, which is not yet peer reviewed, also found that for J&J recipients, antibody levels were higher if they received a Moderna or Pfizer booster rather than a J&J booster.

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