The stated efficacy/protection percentages that have been presented so far have been for the reduction of _symptoms_.
There haven't been any studies on vaccines preventing infections, probably due to lack of resources for testing everyone in a trial multiple times.
I spent last night puzzling over what "efficacy" means vis a vis this video: https://www.technologynetworks.com/immunology/videos/covid-1...
The author explains that the efficacy number is derived from the the number of the number of people in the control/placebo group infected divided by the total number of infections in the study.
76% efficacy means that, for a given population of people who contracted a disease (ignoring all uninfected), 24% were vaccinated (vaccine failures), 76% were not vaccinated. It has nothing to do with reduction of symptoms.
I think this is unintuitive because the "real" solution that laypersons want is, what percentage of vaccinated people exposed to a disease get infected? We can't measure that directly because we can't just expose a bunch of folks to Covid and hope for the best. But if the sample of placebo and vaccinated people is truly random, this would appear to arrive at the same ratio. (re: when I said "ignoring all uninfected"? in a good sample, the ratio of unexposed vaccinated and control units should be about the same)
We can, but medical ethics hasn't caught up yet. I would participate in a challenge trial, for instance.
Me too. And nearly everyone I know in my risk tier.
We had an entire globe of low-risk people willing to be part of the most acute spread, whether for research, for personal immunity, or to be able to isolate for a defined time to protect loved ones, and we squandered it in favor of pseudoscientific horizontal interdictions like lockdowns. It's really an incredible abandonment of basic principles of public health.
But there's a lot of information we left on the table. We had an opportunity to systematically formulate a controlled acute spread, studying the virology in a longitudinal way, studying the immune response in a more intimate and controlled way (from antibodies to the immune response after antibodies fade), and to examine the prevalence and role of innate immunity.
Beyond research, we had a chance to have tens of millions of people with verifiable immunity in Spring or Summer. People who then were in a great position to render aid to the marginalized communities who are instead bearing the brunt of lockdowns.
Instead, we traded all that for zero upside. And we have to deal with the enormous side effects of the horizontal interdiction as well.
It would mean handling live virus, which requires a Biosafety Level 3 facilities.
And, it's not going to get your vaccine approved any quicker.
Quite the example of the asymmetry. If you engage with the problem you have to operate absolutely perfectly. Way better not to engage with it and kill a few hundred thousand people. After all, no one can blame you for that part.
And of course it's not going to get the vaccine 'approved' quicker because yeah, 'approval' is also subject to the same people. But it will let us know if it works and whether it hurts.
Those things are not true alternatives.
I said "it's not going to get your vaccine approved any quicker" in the hope that you would understand: vaccines have reached the point of global distribution without doing the additional deliberate harm of intentionally infecting people.
Of course I am healthy, my family has had the vaccine or the disease and punched through, so I don't really care all that much.
The bottleneck has generally been manufacturing rather than approval so far. It may shift to distribution.
There is so much confusion and missinformation flying around, when even here on HN there is discussion about the meaning of basic numbers.
(but please carry on discussing it)
It's very difficult to get even a basic grasp of the details because you need to grok some complex statistics, biology, and public health to really dig in. Journalists sure aren't going to get the nuances so of course you have to read the academic literature.
Wouldn't that make a vaccine that does nothing 50% effective, instead of 0% effective (which is what one would expect)?
Furthermore, let's say you had 200 infections, split equally between the junk and the placebo.
So yeah, 100 / 200 = 50% effective. A coin toss, which is to say, no better or worse than not getting the vaccine.
Again, this isn't measuring "what one would expect" (how many vaccinated people, exposed to the virus, get the disease), it's "what proportion of vaccinated people get sick relative to unvaccinated people." (again IANAD)
If you measured efficacy as "1 - (vaccinated infections / unvaccinated infections)", it would be much more intuitive, and you could even get a bit of negative efficacy in the case where your vaccine did nothing.
This was posited (but has not been confirmed) as one of the reasons it was posting lower numbers - it was catching some asymptomatic cases
This study has looked at that. From the press release: "Analyses of PCR positive swabs in UK population suggests vaccine may have substantial effect on transmission of the virus with 67% reduction in positive swabs among those vaccinated"
If that's the reduction of symptoms here, ok.
You won't have neutralizing antibodies in the mucosal surfaces in the upper respiratory tract which would be required to completely prevent infection.
You will have NAbs in the bloodstream which should very effectively isolate the infection to the upper respiratory tract. Immune responses will also be primed so that the infection in the upper respiratory tract will be dramatically reduced. In many cases though the infection will be detectable via rtPCR but that won't be significant since the person won't be symptomatic, won't "feel sick" (or very sick) and will be very unlikely to transmit the virus. It should also entirely cut out the multi-organ involvement of covid since the neutralizing antibodies in the blood will prevent spread to the lungs/kidney/heart/brain/etc.
Testing via rtPCR for "infection" would be an expensive waste of time in a vaccine which isn't expected to confer that level of protection. And when it failed to confer that level of protection you're left trying to explain why that low number doesn't matter to a population expecting some kind of medical miracle.
Instead they watch for symptoms and then they confirm that is a SARS-CoV-2 infection via rtPCR, and this is the typical "efficacy number" which is reported (I think the initial Oxford trial results did report the results of randomized rtPCR testing so their numbers were dramatically lower, which has caused all kinds of confusion since its not apples-to-apples with the mRNA vaccine results).
Reduction in transmissibility is more difficult to determine which is why those numbers aren't reported, it is assumed that reduction in symptoms correlates with reduction in transmissibility. So none of the vaccine trials can conclusively rule out asymptomatic spread in vaccinated individuals. However since the people are being followed over time what is caught is any infection which subsequently produces symptoms. So the vaccinated asymptomatic individuals would be truly asymptomatic and not just presymptomatic. Dramatically cutting down symptoms is expected to be a pretty good proxy to dramatically cutting transmission.
Relevant quote from a recent BMJ article on truly asymptomatic transmission:
> The transmission rates to contacts within a specific group (secondary attack rate) may be 3-25 times lower for people who are asymptomatic than for those with symptoms.1121415 A city-wide prevalence study of almost 10 million people in Wuhan found no evidence of asymptomatic transmission.16 Coughing, which is a prominent symptom of covid-19, may result in far more viral particles being shed than talking and breathing, so people with symptomatic infections are more contagious, irrespective of close contact.17 On the other hand, asymptomatic and presymptomatic people may have more contacts than symptomatic people (who are isolating), underlining the importance of hand washing and social distancing measures for everyone.
https://www.bmj.com/content/371/bmj.m4851
The title study here on HN on the Oxford vaccine is pretty clear that they're looking for "primary symptomatic COVID-19" which means they're not screening for asymptomatic infection, they're waiting for symptoms, then confirming.
They found that one shot conferred good protection (76%) for at least 90 days post vaccination (after the first 2 weeks) with little waning and some evidence that it gets better. They also found that the BEST boosting interval was 12+ weeks or more, reaching 82% efficacy. This matches what I've heard some virologists yap about informally online that longer boosting intervals are generally what is recommended (more or less letting the learning immune response bake longer while letting the immediate response to the vaccine vector wane) but the early studies used short intervals due to pandemic driven concerns around giving health providers and the elderly the best immunity in the shortest period possible. Now that we're transitioning to needing to vaccinate literally everyone the message may unfortuntely shift in ways that make people suspicious.