I'm planning to get a Pfizer dose, two months after getting a J&J dose. Is there any reason to think this is unsafe? Also, are there good reasons to think it is safe, beyond my current stance of just "I don't see any reason why it would be dangerous"?

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Jun 04, 2021


Opposite.  Them getting to your immune system from slightly different 'directions' likely increases effectiveness slightly, especially for the adenoviral vector vaccines where vector immunity might be an issue.


Jun 03, 2021


Part of the risk of a any drug is that you might be alergic to any ingridient. If you take multiple different drugs with ingridients, there's a higher chance you increase the chance of being faced with an ingridient that you have a bad reaction towards. I don't think that's a huge concern in this case. 

One problem with taking the same vaccine multiple times is that your body might build defenses against ingridients in the vaccine besides the spike peptide which makes the second dose less effective. As far as I remember the Russian vaccine uses different virus vectors for the first and second dose to counteract this. 

Given the situation we have in Berlin where we have at the moment more AstraZeneca vaccine, I got AstraZeneca as the first shot. My doctor recommended the BioNTech vaccine for the second shot because it might increase protection against new strains like the South American one. While giving that recommendation my doctor didn't think there were any risks regarding mixing that were worth telling me about. 

I think the difference in risk are likely tiny between mixing and not mixing. I would expect that it's more likely that mixing is reducing risk then increasing risk.

I agree in most cases, but here specifically, I’m worried that doctors are just going to follow CDC guidance and say something like “vaccine efficacy cannot be directly compared, and one J&J counts as fully vaccinated, so current guidelines say no, no more dose”. And it would cost my company around $500 to go to a doctor’s office and get their advice, which seems like a waste.

Also, I’d already signed up for the appointment before posting this question, planning to go! So the alternatives here were not “ask LW or ask my doctor”, but rather “ask LW or ask no one”. The advice here is better than the no-advice option I would have gone with if LW didn’t exist, or deleted this type of question.

0Stuart Anderson3y
2Maxwell Peterson3y
Yup yup - I was wondering if there was some weird less-known but persuasive reason it might be dangerous, so thought I’d do a double-check here. Cheers!

He is not asking to any random forum on the Internet, he is asking to a community of rationalists with many well-informed people about many different topics. 

-14Stuart Anderson3y