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I realize there are several different mRNA vaccines. I would be happy to know the ballpark figure for any of them.

As a follow-up, is it known about what percentage of injected mRNA strands are successfully translated into proteins?

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    $\begingroup$ Check meta.stackexchange.com/questions/66377/what-is-the-xy-problem - it seems like this question and your other recent question might suffer from this issue. What is motivating the questions you're asking here? What are you hoping to get from these numbers? $\endgroup$
    – Bryan Krause ♦
    May 5, 2021 at 4:14
  • $\begingroup$ Partly it's pure curiosity. I couldn't find this information anywhere. Regarding my other question, after a night's sleep I realize mRNA must be translatable more than once, or it would not be possible for a virus to replicate more than one copy of itself. Still, what about "friendly" mRNAs? What prevents an mRNA from being translated indefinitely? I'm just curious! But yes, you're right that I am also wondering about how the total number of spike proteins generated by an injection would compare to those encountered in a natural infection. $\endgroup$
    – Brian Rak
    May 5, 2021 at 14:31
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    $\begingroup$ I think it would be better to ask one of those intended questions more directly, rather than the one you asked - that's kind of where the XY problem comes in where you are asking something that you think will get you closer to answering your intended question, rather than starting with the intended question. $\endgroup$
    – Bryan Krause ♦
    May 5, 2021 at 17:06
  • $\begingroup$ Thanks, I appreciate that. But I'd also just like to know the answer to this question. For what it's worth, I think it would add value to everyone to be able to search for this specific question and find a simple answer. Maybe I'm just searching with the wrong terms, but I was not able to find it. $\endgroup$
    – Brian Rak
    May 5, 2021 at 19:36

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Well, we can work this out empirically.

We know that the average molecular mass of a base of a RNA is 339.5 g/mol.

Despite this, to calculate the approximate molecular mass of a single-stranded RNA molecule, you multiply the number of bases by 320.5 (because some bases are more common in sequences than others) and add 159 (same source). This means for a single-stranded molecule of 1000 bases, it will have a molecular mass of 320,659 g/mol. The Pfizer vaccine has a sequence of 4284 bases.

4284 * 320.5 + 159 = 1373181 g/mol.

The Pfizer vaccine has 30 ug/shot (PDF, see page 27 under "Description") or 30x10-6 grams

number of moles = mass/molar mass.

n= 30 x 10-6 grams/1373181 g/mol

n= 2.185 x 10-11

number of molecules = n (above) x Avogadro constant (6.022 x 1023)

Number of molecules = 1.316 x 1013

Now this is a ball-park figure because the RNA isn't actually RNA it has had some special additions to the uridines that make it less susceptible to immune regulation, replacing the uridines with 1-methyl-3'-pseudouridylyl (see Wikipedia link to structure above). However, I believe this alteration to the mass, will not alter the number substantially; it'll still be in the 10 trillion range.

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    $\begingroup$ The 30 mcg/dose in the Pfizer pdf indeed refers only to the RNA. The lipid nanoparticle etc. is counted separately. In case anyone else was wondering that. $\endgroup$
    – timeskull
    May 6, 2021 at 14:15
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    $\begingroup$ Wow, thank you, @bob1! That is a truly tremendous number. So that would mean that, seeing as we only have 30-40 trillion cells, depending on the uptake of the mRNA into cells and the number of times each strand is translated, you could end up with more spike proteins floating around your body than your total number of cells. What an incredible surface area for your immune system to notice. Awesome! $\endgroup$
    – Brian Rak
    May 6, 2021 at 14:55
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    $\begingroup$ Also, for comparison, this source (ncbi.nlm.nih.gov/pmc/articles/PMC7685332) says that at peak infection, a person can have 1 billion to 10 billion virions in their body. $\endgroup$
    – Brian Rak
    May 6, 2021 at 15:22
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    $\begingroup$ @BrianRak - The data on how much is produced is proprietary. I suspect that the 30 ug is the amount of RNA, definitely not all of that will be packaged, some will be lost to degradation (transport, preparation etc), and some proportion won't make it into cells. My experience using plasmids and liposphere preps (common in bio labs, but not the same as the Pfizer ones) is that somewhere between 30 and 90% of cells in a dish will be transfected, but it will definitely be less than that in vivo. There are too many variables to answer the second part of your question in the OP. $\endgroup$
    – bob1
    May 6, 2021 at 20:28
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    $\begingroup$ @BrianRak to address your second comment - in culture (ideal conditions) you get about 10^6 (1 million) - 10^7 infectious particles/ml, so these numbers seem surprisingly low to me, but I guess it will be a staged infection - not all cells getting infected at once, unlike in the lab where a whole flask of cells will infect at the same time. $\endgroup$
    – bob1
    May 6, 2021 at 20:31

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