According to the CDC's page on the safety of J&J vaccines, the reported efficacy rate of the vaccine is a staggeringly low 66.3%.

That said, the government is still promoting and touting the J&J vaccine as a reliable and effective way to protect oneself against the effects of the COVID-19 virus.

In a report published just yesterday, the CDC published an official study on 32,867 COVID vaccinated people and found numbers that closely matched those of the clinical trials mentioned above, in that Moderna is 95% effective at preventing hospitalization, followed by Pfizer at 80% and J&J at 60%.

So if the numbers are correct, why is J&J still touted as an effective protection against COVID-19 still? 60% isn't exactly the greatest confidence booster -- that's almost at the level of a coin flip. How can the J&J vaccine shot be effective against COVID-19 if it only has a ~60% efficacy rate? Pfizer/BioNTech and Moderna's vaccines offer a much more solid guarantee, but 60% for J&J?

How can 60% be considered effective?

  • 6
    This is a more suitable Q to ask on medicalsciences.stackexchange.com/questions Your're not really disputing any data/figures, just quibbling with how the CDC phrases their findings. I'd also add that efficacy for mRNA vaccines seems to drop faster over time compared to the AD-vectored ones, from other recent studies (including some by the CDC), see e.g. medicalsciences.stackexchange.com/questions/28894/…
    – Fizz
    Sep 11 at 6:59
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    You really need to distinguish effectiveness against infection and against serious illness/hospitalization and death. Those are very different numbers, there is not a single effectiveness number for the vaccines
    – Mad Scientist
    Sep 11 at 8:11
  • 60% would reduce the number of deaths say from 100,000 to 40,000. But it’s better: The number of people infected would also be reduced say from 10,000,000 to 4,000,000. And these would infect 60% less, but 4,000,000 in contact with vaccinated people infect 40% of 40% of the numbers that 10,000,000 in contact with unvaccinated people will infect.
    – gnasher729
    Sep 21 at 18:15

60% isn't exactly the greatest confidence booster -- that's almost at the level of a coin flip.

That's actually not quite so.

So, for example, let’s imagine a vaccine with a proven efficacy of 80%. This means that – out of the people in the clinical trial – those who received the vaccine were at a 80% lower risk of developing disease than the group who received the placebo. This is calculated by comparing the number of cases of disease in the vaccinated group versus the placebo group. An efficacy of 80% does not mean that 20% of the vaccinated group will become ill.

it does mean that in a vaccinated population, 80% fewer people will contract the disease when they come in contact with the virus

VE is calculated as (ARU - ARV) / ARU. If the ARU is say 0.7, i.e. without a vaccine you get ill 70% "of the time" (more correctly 70% of the population would--something like this was estimated early in the pandemic) then a VE of 0.6 means that that ARV is just 0.28, i.e. only a bit more than a quarter of the vaccinated would get infected. And that's much better than a coin flip. So ARV, which is really what you want to compare with the coin flip, really depends both on the ARU and VE.

Also, the VE numbers you're talking about concern hospitalization... and the ARU for that is pretty far from a coin flip to begin with--something like 5% (based on an IHR of 7% among the infected, and assuming 70% of the pop gets infected). So, in this latter case, comparing two numbers (ARU, ARV) that are far from a coin flip... with a coin flip is not exactly insightful. ARV would be 0.02 in this case, i.e. your "hospitalization chance" drops from 5% to 2% when vaccinated, under these assumptions. That may not look like much (absolute) difference for individual protection, but it does mean needing less than half as many hospital beds etc.

Somewhat o/t, but in a 3rd world country (that can't afford mRNA vaccines) even the J&J vaccine could make quite a difference as anyone needing hospital care and not getting it at all is fairly likely to die; see what shortages of oxygen have caused in such counties.

And hospitalization isn't the only thing worth considering. Deaths were not considered in that CDC study you're quoting from, but the J&J vaccine seems to do better in that regard:

in early August, a clinical trial that followed nearly 500,000 health care workers in South Africa found that the J&J vaccine was 71% effective against hospitalization and 95% effective against death due to the delta variant.

I'm not going to comment on how the CDC chooses to phrase their findings when comparing vaccines, but I'll just add that efficiency at single point in time is not the whole story.

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    Could you include some definitions for the abbreviatations? VE, ARU, ARV, and IHR aren't familiar to most of us.
    – Mark
    Sep 11 at 16:38
  • But your numbers do indicate that the coin flip metaphor is not too far from correct: If 5% of the population "win" a hospitalization ticket and - thanks to vaccination - use a coin flip to decide whether they actually need it, we end up with 2.5% hospitalization (instead of 2%, but then again, a 50% coin flip is not a 60% thing) Sep 12 at 5:47
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    @HagenvonEitzen: but not being vaccinated has 100% chance in that conditioned case. So it's not clear why the coin flip is the relevant comparison. You could say that it goes from a "sure thing" to something like a coin flip (even in that conditioned case), but even that's an improvement. I mean, you do have a point, but it's coin-flip vs 100%.
    – Fizz
    Sep 12 at 11:29
  • If I was supposed to be told “sorry man, you are going to die from Covid” and instead I’m told “sorry man, there’s a 40% chance that you are going to die from Covid”, the second is a huge improvement.
    – gnasher729
    Sep 26 at 11:54
  • If at some stage there is a 100% chance to die outside hospital, and only 40% inside a hospital, and there are 1000 hospital spaces, and 3000 get badly ill, you have 2000 + 400 = 2400 deaths. If a vaccine is 60% effective and you have only 1200 badly ill then you have 200+400 = 600 deaths. So the effect of vaccination can be much greater.
    – gnasher729
    Sep 26 at 11:58

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