From what I understand, updating an mRNA vaccine is trivial. According to this answer, no or small clinical trials would be needed to update the vaccine, and updating production would also be trivial. Why, then, are we still producing the original vaccines if their efficacy is decreasing given the new variants?

  • You ask different questions in your question title and body: 1) Why aren't mRNA vaccines being updated for new variants? 2) Why are we still producing the original vaccines.
    – Armand
    Commented Jul 8, 2021 at 16:56
  • What research have you done to verify that mRNA vaccines are indeed not being updated for new variants?
    – Armand
    Commented Jul 8, 2021 at 16:57
  • @Armand, if you search for it, you'll find that all the pharma companies are developing "boosters", not updating their existing vaccines.
    – herman
    Commented Jul 9, 2021 at 6:18
  • I suspect there's no difference between a "booster" and an "updated existing vaccine".
    – Armand
    Commented Jul 9, 2021 at 8:12
  • Exactly. So why not get the booster as the vaccine? That is my question. I hope eventually it will be that way, but it seems not at the moment.
    – herman
    Commented Jul 9, 2021 at 10:16

2 Answers 2


Trivial in concept, sure, but not necessarily trivial in practice. It's not about just producing a handful of doses in a proof-of-concept; if you want to produce a different version of a vaccine at scale it means either building a bunch of new equipment or retooling a previous production line to make the whole vaccine. Since only a minority of people are vaccinated world-wide, it makes sense that the original vaccines continue to be manufactured since these are still effective against the variants that are being transmitted (maybe not as effective as they can be, of course). Right now, it's almost certainly more important to get any vaccine into arms rather than the ideal vaccine.

That said, it would be false to state that vaccines to target variants are not in the pipeline. Pfizer announced today, for example, that they are developing a booster to target the delta variant. Presumably other vaccine manufacturers are doing so as well - not everything in pharmaceutical research labs gets reported. Manufacturers have to make cost-benefit analyses about what variants to target. Had they prepared a variant booster a few months ago it might have targeted the alpha variant rather than delta variant, for example; today, it seems targeting the delta variant is more pressing.

I'd also add that, as far as I know, no regulatory agency has declared that no clinical trials of an "updated" mRNA vaccine is necessary, or publicly specified what data are required, so I think that's just speculation so far, although well-informed. If descendants of COVID-19 become endemic like influenza, then it seems likely that a regulatory framework similar to that for the annual influenza vaccine would allow new formulations to be distributed without large-scale testing (like in this Q&A: Flu vaccine paradox), but we aren't there yet.

  • Thanks for the answer. I guess my question is about the retooling part. The vaccine is not made using a die or a mould. I would think that the process and equipment remain the same, regardless of the internal mRNA sequence itself, as per e.g. pubmed.ncbi.nlm.nih.gov/33771389. The issues of scaling should remain the same when changing a few A, C, D, and U's around. But yes, maybe new trials are needed.
    – herman
    Commented Jul 9, 2021 at 6:27
  • 1
    @herman Unless new guidance is issued by regulatory agencies or it's used only in places with little or no regulation then new trials in some form are definitely needed.
    – Bryan Krause
    Commented Jul 9, 2021 at 12:43
  • It is still not clear whether the updated version of Pfizer's vaccine is tested/marketed only as "booster", or it will become the new base standard. I.e. would a new patient has to go through 2 doses of the old vaccine before having a chance of receiving an updated version?
    – Alexander
    Commented Sep 1, 2021 at 16:46

Here is the best answer that I have found, from Dr. Katelyn Jetelina, MPH PhD, writing as Your Local Epidemiologist

If we need another vaccine, we can do this incredibly quickly. Thanks to the new biotechnology, mRNA vaccines are really easy to alter. Once the minor change is made, only 2 dozen people need to enroll in a trial to make sure the updated vaccine works. Then it can be distributed to arms. Because the change is small, an updated vaccine doesn’t need Phase III trials and/or regularity approval. So, this whole process should take a max of 6 weeks.


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