I was pretty bummed out when I read that neither the Pfizer nor the Moderna vaccines necessarily prevented the transmission of SARS CoV 2. I don’t remember where I first heard about this but here’s one cite:
neither the Pfizer nor the Moderna vaccine trials tested whether the vaccines prevent people from being infected with the virus. Those trials, instead, focused on whether people were shielded from developing disease symptoms. That means that it’s not clear whether vaccinated people could still develop asymptomatic infections — and thus still be able to spread the virus to others.
So when you hear that these are 90%+ effective it means 90% effective at preventing symptomatic infections. It doesn’t mean 90% effective at preventing infections in general, which I thought was the whole point.
It’s still possible that the vaccines do cut down on transmission, but it hasn’t been tested–it was not part of the vaccine studies and trials AIUI.
Drastically lowering the cases of serious life-threatening cases of COVID-19 would be fantastic so don’t look a gift-horse in the mouth, and all that! It’s just that I thought it was all about preventing transmission.
This means that even after you are vaccinated you will still need to wear a mask. Americans are already really bad about wearing masks–can you imagine how much worse it will be after they and most others around them have been vaccinated?
Is this the way vaccines normally work? I was always under the impression that flu, shingles, pneumonia, polio, smallpox, etc. vaccines inoculated you from getting infected. Do those vaccines prevent transmission or do they just cut down on the severity of symptoms?
I agree. People with no symptoms are probably shedding the less virus that someone who is coughing a lot. The thrust of my post was more that I wonder how many people realize these vaccines weren’t even designed to deal with transmission of the virus.
Are most people like me in that they figured that’s what viral vaccines generally do? Prevent the spread of viral pathogens?
Yes, most people probably think that. But these vaccines were designed to produce a robust immune response. “these vaccines weren’t even designed to deal with transmission of the virus” isn’t really accurate. The hope is that a robust immune response will lower transmission.
This is highly misleading. It’s not as though preventing symptomatic infection and preventing any infection are mutually exclusive or uncorrelated objectives.
All vaccines are designed to produce an immune response against the pathogen. A more robust immune response is more likely to do all the things we want - preventing disease, preventing asymptomatic infection, lowering transmission.
It’s not that these vaccines were designed to achieve some of these things and not others. But when time is of the essence, the most straightforward thing to measure in a large trial is the incidence of symptomatic infections. So that’s the initial data that we have. We’re not going to waste a year before starting vaccination, waiting for more data to figure out with absolutely certainty that we have the best conceivable vaccine, when we can definitely save lives by starting now with what we already know is safe and definitely will save lives.
Now it’s possible that we might just get really unlucky, and although these vaccines do produce a robust immune response that stops serious disease, for some strange reason they may have little or no effect on asymptomatic infection rates or on transmission. It’s sensible for scientists and authorities to point out this uncertainty. But a priori that’s not a likely outcome. All these articles that you’re reading are just saying that we don’t know yet. And in the phase when few people are yet protected by vaccines, given that uncertainty, people who have been vaccinated should continue to follow social distancing protocols.
I am not a virologist, but if we eliminate the symptomatic infections, then what is the remaining problem? If we are passing around a virus one to the other that causes no issues then carry on, no?
It will take a long time logistically before everyone is vaccinated, and some people can never be vaccinated for medical reasons. It will be much better if vaccination also reduces asymptomatic infection rates and concomitantly reduces transmission, in order to slow community spread and perhaps achieve herd immunity well before everyone is vaccinated.
Fair enough. I didn’t properly address the nuances. I don’t want to mislead on a subject as important as this. Mostly I was just surprised that these vaccine studies did not indicate what I thought they did (and IMO, most people would think they did).
I thought the research showed that the vaccines were 90+% effective at preventing infection. I made an assumption that I believe most people did. Turns out the vaccine research shows they are 90+% effective at something else (preventing symptomatic infection, not infection itself). And that is fantastic because it will save lives.
Even though this has been reported, I think a lot of people, Americans especially, have a bit of a surprise coming to them. I think we’re going to see a lot bigger problem getting people to wear masks after the vaccinations start in earnest.
We certainly need to wait until at least all the high risk groups are vaccinated. By then we’ll probably know a lot more about the effect on transmission anyway. But I don’t think it’s as depressing a prospect as you imagine.
I mean, personally I think shaking hands should have stopped as soon as we discovered the germ theory of disease, so I feel no inclination whatsoever to engage in unnecessary physical contact with strangers ever again. But I think we’ll be getting somewhat back to normal in many ways by summer.
And I think that it most likely does. But my question as far as that is: why didn’t they give periodic COVID tests to the asymptomatic test subjects? Isn’t the infection rate a critical piece of data?
Time and resources. It’s tens of thousands of subjects, and the presence of infection is not a direct measure of what you care about anyway - after effect on disease, what matters is the effect on transmission.
Emergency, worldwide, expedited research into a deadly, novel virus was always going to be astoundingly expensive, wasn’t it? I don’t think there was much stinginess when it came to funding.
And you’d only have to test a representative sample of that cohort, not all of them, right?
And I guess I’m missing something (seriously, not sarcastically)… wouldn’t you measure a vaccine’s “effect on transmission” by testing for incidence of transmission to the cohort? IOW, test for the presence of the virus?
There are 3 things here.
(1) Whether the vaccine protects against disease (symptomatic infection).
(2) Whether the vaccine protects against asymptomatic infection.
(3) Whether the vaccine prevents transmission from vaccinated people to others.
(1) and (3) are the things we care about.
(1) is easy to measure directly, and that was the metric in the trials, that’s the 90%+ figures that are being reported.
(3) cannot be measured directly.
You can measure (2) directly, although it takes a lot more resources than (1). Repeated PCR tests for tens of thousands of people. And (2) is not exactly what we care about. Sure, you can make the argument that (3) is probabilisitcally correlated to (2), so (2) would be useful data to have. But if we’re just talking about correlations, (3) is also correlated to (1).
How? The labs are busy full-time doing testing and contact tracing in the real world. There isn’t spare capacity.
And would it work? The PCR swab test used for most testing has been validated for detecting symptomatic and pre-symptomatic cases. Like the vaccine, it’s poorly validated for sub-clinical asymptomatic disease.
And why is the PCR swab test poorly validated for sub-clinical asymptomatic disease? Well, for a start, the antigen tests for detecting past COVID infection have not been validated for sub-clinical asymptomatic disease…
AstraZeneca tested during their study. They didn’t seem to think it was a waste of money.
Reading up on this last night I saw an interesting article talking about the advantages the AZ vaccine had over Pfizer and Moderna. Aside from its logistical advantages it also had the advantage of having been analyzed for infection incidence during the study which Pfizer and Moderna didn’t do. This was made out to be significant so I sure wish I could find that.
Here is what I can find right now that reflects that viewpoint but not as well:
The analysts highlighted weekly swabbing to detect Covid-19 among participants involved in AstraZeneca’s trials — not just confirmation of suspected cases by symptoms as in U.S. trials.
The Oxford-AstraZeneca coronavirus vaccine has a “distinct comparative advantage” over other leading candidates, the editor-in-chief of The Lancet medical journal said Wednesday.
…
The data also suggested that the vaccine can help reduce the spread of Covid-19as well as preventing illness and death.
[Emphasis mine]
In other words, as well and functioning as the American vaccines do in preventing serious symptoms, the AZ vaccine also cuts down on the spread of the virus. Some people seem to find this more important than some of you guys here.
Nobody has suggested that reducing transmission is not important.
But again you’re wording this in a misleading manner as though we know the Pfizer & Moderna vaccines do not do this. We do not have the data does not mean that, it just means we don’t know. Maybe the decision not to try to gather data on asymptomatic infection as early as AstraZeneca was a mistake, but it implies nothing about the ultimate outcome.
Since all these vaccines target the same Spike antigen, the AstraZeneca data increase our confidence that the Pfizer & Moderna vaccines probably also reduce transmission.
Yes I think it was a mistake and mistakes happen, sure. Mitigation of symptoms is important, of course. But if there’s no transmission, there’re no symptoms to mitigate, right? So that has to be of the greatest import. I’m glad AZ recognized that.
I mean really… how do you not test for viral transmission in a vaccine study?
No, this is quite confused. From the perspective of the person being vaccinated, what matters first is protection against disease. The other thing we’re talking about is reducing transmission to other unvaccinated people from people who are vaccinated. The latter is important in reducing community spread, but that will only occur after a large number of people have been vaccinated.
For a disease that is only serious for a small proportion of the population, in the early stages when we need to rush out a vaccine quickly, and we can only vaccinate a small proportion of the population at first, protection against disease for high risk people will be what saves lives.
But in any event you seem to be just completely ignoring the points that have been made that these objectives are correlated, they are not totally independent outcomes. If we have evidence that a vaccine produces a robust immune response that reduces the incidence of symptomatic disease by over 90%, it it highly likely that it will also reduce transmission at least to some degree.
And again you’re ignored the point that AstraZeneca didn’t directly measure transmission either. They measured asymptomatic infections rates. Sure, more data is better, but what they measured is still only something that is correlated with reducing transmission from vaccinated people.