Is there any reason NOT to vaccinate with more than one brand of COVID 19 vaccine? For example, 2nd Pfizer in January and JNJ in April. Nothing returned via Google.

Clarification: the context is that two complete dosages (JNJ requires 1 dose, Pfizer requires 2, Moderna requires 2) of different vaccines are under consideration for the question. US CDC guidance advises completing a regimen with the same vaccine.

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    How about the limited number of vaccines to go around? Seems a bit selfish for someone to hog more than they need isn't it?
    – Bryan Krause
    Feb 28, 2021 at 3:10
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    Another reason is you'll be the one finding out if there's a reason.
    – Carey Gregory
    Feb 28, 2021 at 4:02
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    Depending how much your immunity has waned (or not) the 2nd vaccine could have more severe side effects. This is already the case with the 2nd dose of the vaccines which need a booster. Mar 2, 2021 at 9:18
  • By "more than one" in the title, do you really mean "one shot of A and one shot of B" to complete a 2-shot course? Note that the Johnson & Johnson vaccine is a single course so your question is quite unclear on this point and it seems like you are asking about two separate courses of vaccine.
    – Bryan Krause
    Mar 10, 2021 at 19:16
  • @BryanKrause Thanks for the question, does the update clarify? The context is Brand A, then Brand B. Please feel free to add edits that clarify to the posting
    – gatorback
    Mar 11, 2021 at 16:53

1 Answer 1


"Is it a good idea to mix and match COVID-19 vaccines? Experts aren't so sure"


Barry Pakes does not have a safety concern per se but is concerned about efficacy being compromised. Later in the article Dr. Isaac Bogoch, though open to the idea, has a concern about safety and efficacy alike. Both experts admit that more research and data is needed.

Britain Opens Door to Mix-and-Match Vaccinations, Worrying Experts" https://www.nytimes.com/2021/01/01/health/coronavirus-vaccines-britain.html

"Some scientists say Britain is gambling with its new guidance. “There are no data on this idea whatsoever,” said John Moore, a vaccine expert at Cornell University. Officials in Britain “seem to have abandoned science completely now and are just trying to guess their way out of a mess.”

CDC practically agrees here: https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html#Interchangeability

"Interchangeability with other COVID-19 vaccine products either of the currently authorized mRNA COVID-19 vaccines can be used when indicated; ACIP does not state a product preference. However, these mRNA COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products. The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product."

If certain countries end up requiring certain vaccines for entry [assuming they make it mandatory] then it would complicate the matter all the more than it already is. It does not seem advisable.

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