My assessment:

  • People who can easily continue to guard against significant COVID risks for several weeks without much downside other than quality of life should wait several weeks for Pfizer or Moderna.
  • (People who have to expose themselves to a non-trivial amount of COVID risk no matter what should take the J&J vaccine if they'd have to wait several more weeks for Pfizer / Moderna. I haven't run the numbers on this, but at some point I'd expect the additional risk exposure from being unvaccinated for several weeks to outweigh the difference in efficacy.)

My rationale:

1. Moderna and Pfizer provide significantly better protection against non-severe infections.

  • J&J provides:
    • 28 days after the injection: 66% protection against moderate to severe COVID infections (72% "in the United States", but I don't know to what extent that is robust to further spread of foreign variants in the US) and 85% against severe disease [1][2]
    • 48 days after the injection: 100% protection against severe COVID. (I don't know what 100% protection means, exactly - a commenter pointed out that there is no such thing as 100% protection - but for the sake of argument, let's say it's close to that.) [3]
  • Moderna and Pfizer provided 94.1% and 95% protection against any symptomatic infections generally after the 2nd dose [1]

2. I'd expect that even non-severe infections increase your risk of long-term lingering effects (in addition to being fairly unpleasant in the meantime, but I'm less concerned about that). 

  • I don't have great evidence for #2 yet. While mild infections have a non-trivial risk of long COVID [4], it seems like even initially asymptomatic cases account for about a 3rd of long-COVID cases [5]. I would hypothesize that the risk of long COVID is significantly less for asymptomatic cases than for symptomatic cases, but haven't researched that much yet.

Zvi said in his 2/4 COVID post, "I’d pay a substantial amount to get Pfizer or Moderna instead of J&J if I could get either one today, but given the choice between waiting and taking what’s available, I will happily accept the J&J vaccine now rather than hold out for Pfizer or Moderna."


What am I missing? Is this just a difference in the weight we place on resuming higher-risk activities sooner rather than later? Or am I overplaying the superior efficacy of the Pfizer and Moderna vaccines?












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I jumped at the chance to get J&J even though I'm not a essential worker or anything. I think the disconnect between our intuitions is here:

People who can easily continue to guard against significant COVID risks for several weeks without much downside other than quality of life should wait several weeks for Pfizer or Moderna.

As was discussed a bunch in my post on lockdown, the quality of life & mental health impact can be really massive. A marginal month may not seem like a lot if you are really just doing totally fine in lockdown and don't have anything in particular you want to do, but if you are actively suffering all the time, another month feels like forever. Also, for me, waiting a month would mean that I would see my niece for the first time at 3 months old rather than 2 months, which is quite a big difference at that age.

Furthermore, I'm young and healthy, so getting a slightly less effective vaccine probably just shouldn't matter to me that much, when my risk was already so low to begin with. And I wouldn't be surprised if people who get J&J now can get moar vaccinated later (either a J&J booster shot or stacking an mRNA vaccine on top of J&J), so I'm not convinced that the choice I make right now matters that much.


Also I'm pretty skeptical that J&J provides 100% protection at any point, and your source did very little to convince me. 0 and 1 are not probabilities?

I think "100%" in this context means "close enough to 100% than we can't detect the difference".

Reasonable; looking at it again, '0 and 1 are not probabilities' was not my true rejection at all. Mostly I was just surprised to see such an extremely good result from the vaccine that everyone seems to agree is worse.

Thanks, that makes sense. Sorry to hear lockdown was so rough for you, and glad you were able to get the J&J! 

I'm kind of the opposite on both pieces, I think: I'm faring pretty pleasantly under lockdown, but for me, the main things I'm yearning for are relatively high COVID risk -- partner dancing with acquaintances or strangers indoors, and dating people I didn't previously know (and for some reason I keep matching on dating apps with a disproportionate number of people who work in direct patient care roles, haha). So for me it makes sense to delay a bit to get a higher level of protection, and abstain from the riskier activities in the meantime.

For the sake of argument, let's assume that the effectiveness of j&j and moderna/pfizer are 66% vs 95%, respectively, and this effectiveness comes in at the same time. Suppose you keep yourself to a constant risk of x per week, without factoring in vaccine protection, based on the case rates and variants in your area. If n is the number of weeks between getting the j&j vaccine vs the moderna/pfizer vaccine, and m is the number of weeks between getting the moderna/pfizer vaccine and the end of the pandemic, then you have the risk of (1-(x*.33)^(n+m)) if you get the j&j vaccine, and the risk of (1-x)^n * (1-(x*.04))^m if you get the moderna vaccine.

If I was offered the j&j vaccine tomorrow, vs the moderna vaccine I have scheduled in 3 weeks, and we assume the pandemic will be over in the first world by september 1st (20 weeks out), and my weekly (non-vaccinated risk budget) is 200 microcovids, then I would be looking at 0.132% chance of covid with j&j vs. 0.093% chance of covid with moderna/pfizer. So, it's worth it for me to wait it out. But, if you think the pandemic will be over in half the time, then it's 0.066% vs 0.085%, and so you should take the j&j vaccine.

For the sake of argument, let's assume that the effectiveness of j&j and moderna/pfizer are 66% vs 95%, respectively, and this effectiveness comes in at the same time.

I think it's important to also point out that this assumption is not true. All of these vaccines seem to have similar effectiveness for the first 3 weeks after the first dose and the major divergence happens after the second dose (and I suspect there would be a smaller divergence if we did two doses of J&J, but of course we have "no evidence" of that).

From a wanting-to-end-the-pand... (read more)

There is also a risk of PEG immunity which will make one immune to lipid nanoparticle vaccine.

I wound up with Pfizer, but I actually would have preferred to get J&J, due to the more established vaccine tech with less risk of allergic reaction.  They work similarly enough (put *NA into your cells, you build the spike protein yourself, and then react to it) that it's hard for me to believe that much of the apparent difference in effectiveness is real.  J&J scored worse, but on a harder test including the newer strains.  So I imagine J&J is comparable to the first shot of Pfizer/Moderna, and although the second shot does make a real difference, the obvious solution is to just get a second shot of J&J.  Ideally you would wait until supply caught up with or exceeded demand, and ideally the places administering it would stop caring at that point whether you already had a shot but might charge you for it.  In the (likely) worst case where they don't allow it if you already had a shot, you could lie.

A lot depends on how much personal control you have of when and what kind of vaccine you get.  If you knew for certain you could wait 3 weeks and get your preferred vaccine, that's probably better than taking J&J today.  But if there's a fair chance that you WON'T be able to - either you'll have to wait much longer or take J&J anyway, you're probably better off just taking it now.

The driving factor is just how much COVID-19 sucks, and the cost of getting it during that voluntary gap.  If you're truly comfortable and truly locked down, then waiting longer is more reasonable, and it also lets people who need it more than you get it sooner.  In that case, delays of up to a few months may be justified.  If you're only mostly locked down (as I am - I still go out briefly a few times a week for things that can't easily be delivered), then delay is riskier and you should prioritize any vaccine, delaying no more than a week or two.

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