4 ms·

No, at the moment "the main purpose of a vaccine" is still not "herd immunity" at all. The Phase 3 trial protocols measured and presented the "efficacy" which i

by acqq 6y ago

No, at the moment "the main purpose of a vaccine" is still not "herd immunity" at all. The Phase 3 trial protocols measured and presented the "efficacy" which is defined as the reducing the chance of the vaccinated getting sick -- that is, merely reducing the severity of disease among those who were vaccinated. https://www.medscape.com/viewarticle/941030?src=soc_tw_201118_mscpedt_news_mdscp_vaccine&faf=1 https://www.medscape.com/viewarticle/941030?src=soc_tw_20111... "In an ideal world, a vaccine would prevent infection entirely and, it follows, also prevent disease and severe disease. But this may be hard to achieve for a respiratory virus vaccine. Animal challenge data suggest that vaccinated animals may still be infected even if they don't experience symptoms. A vaccine that is able to reduce the severity of disease, even if it cannot prevent infection entirely, would obviously still have enormous public health value. Therefore, this is what trials target as their primary aim." Not all vaccines are the same. For mumps, totally different kind of disease, to prevent an outbreak, there was a following calculation: https://vector.childrenshospital.org/2017/03/social-media-mumps-herd-immunity/ https://vector.childrenshospital.org/2017/03/social-media-mu... "since one in 10 vaccinated people are still susceptible to mumps, an overall vaccination rate of 96 percent is needed to prevent an outbreak" For Covid-19, to note from the first source again: "A vaccine that is able to reduce the severity of disease, even if it cannot prevent infection entirely, would obviously still have enormous public health value. Therefore, this is what trials target as their primary aim."

gojomo 6y ago
Yes and no. These vaccines have been formally tested for their ability to protect the recipient, & there is some unquantifiable risk that they'll still get harmless-to-themselves mild infections – especially nasal/mucosal/surface infections – that can still transmit to others. But it's reasonable to also expect the following to be shown when there's more time: * The milder infection makes such infections less transmissible (in terms of duration-of-infectiousness of quantity-of-sheddding) * such superficial infections in the vaccinated don't recur often, or as they recur become ever-milder – because the nasal/mucosal surfaces themselves eventually improve their immunity. So, an extra step is required to achieve the simplified idea of 'herd immunity', but the vaccines is still one step in that direction. So it is still very much the hope & eventual aim of these vaccines to keep enough people alive, with mild easily-recovered infections, that 'herd immunity' (and thus much-lower or almost non-existent rates of infection even in the unvaccinated) is reached.
- acqq 6y ago
  > But it's reasonable to also expect ... - The milder infection makes such infections less transmissible (in terms of duration-of-infectiousness of quantity-of-sheddding) Neither reduced duration of infectiousness nor reduced quantity of shedding by definition protects the vulnerable. It can reduce the speed of spread, but that by definition doesn't even mean that a vaccinated person can visit their non-vaccinated or immune suppressed relative without the mask. For all we know the "quantity of shedding" has to be very low for transmission to provably not occur -- some experts estimate that a single droplet containing only 500 viruses is enough. To compare, the typical tests measure the presence of virus RNA starting with many millions in the sample and the tests do detect asymptomatic persons -- those who don't get sick now. > superficial infections in the vaccinated don't recur often From the studies of other coronaviruses it is known that infections do recur. And finally, we even know that even some percentage of people who get the vaccine become the disease later and are observably sick -- that's the difference to 100 to efficacy percentage (e.g. 5 of 100 who received the vaccine, or every 20th, if the efficacy is 95%). And we can also expect effectiveness (protection of the vaccine in the real world) to be lower than efficacy (reported from trials). In short, for all we know at the moment, the life will continue to be hard for those who don't get the vaccine and those whose immune system can't respond to the vaccine.
  - gojomo 6y ago
    > Neither reduced duration of infectiousness nor reduced quantity of shedding by definition protects the vulnerable. Everything which reduces community prevalence (& case replication rates) protects the vulnerable, at least indirectly. Briefer and lesser shedding of infectious material is also likely to also contribute to milder cases among the unvaccinated - so they acquire natural-recovered immunity, both surface-mucosal and deep, over time with fewer risks to themselves & others. You are correct that simply having recently completed an initial vaccination should not give anyone confidence to immediately visit a vulnerable, unvaccinated person. After all, a surface/mucosal/sub-symptomatic infection that's still transmissible remains a possibility, especially while community infection rates are high. But 6-12 months later, when infection rates are low, and it's quite possible the vaccinated person has already been mucosally-challenged by naturally-circulating virus? At that point, the net effect of vaccines-over-time means the risk of such visits to the non-immune likely returns to the same baseline level that they had in 2018 and before, from everpresent pneumonia/flu concerns. > And we can also expect effectiveness (protection of the vaccine in the real world) to be lower than efficacy (reported from trials). It could go either way. Even in trials attempting blinding, often the vaccinated have a strong hunch (from side effects) they've received the active vaccine - and so take more risks than the placebo arm, thus causing the trial to underestimate actual protectiveness. Also, to the extent early vaccinations could be well-allocated to either most-vulnerable or most-likely-to-spread – subgroups that weren't overweighted in the trials – they could show more effectiveness in disease-prevention. And this only improves as herd immunity grows: in a tiny trial, others' vaccinations have little indirect protective effect, but as immunity rates rise in the community, there's a compounding benefit.
phobosanomaly 6y ago
Oh man, that is severely splitting hairs. You can't have T-cells and antibodies covering every single potential surface area of every cell of every tissue in the body, so there can be places that are infected in the body even though you're totally subclinical and not shedding in a meaningful sense. But such a small infection that is effectively managed by a vaccine-primed immune system is meaningless. That's like saying that a clean living-room floor isn't really clean because you can spot a speck of dust with your magnifying glass. For all intents and purposes, vaccines prevent people from contracting an infection that is clinically meaningful, and that can be spread to others in a way that leads to infection. That's herd immunity. "Herd immunity is a form of indirect protection from infectious disease that occurs when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity." https://en.wikipedia.org/wiki/Herd_immunity https://en.wikipedia.org/wiki/Herd_immunity You're making it sound like vaccinated people are walking around shedding virus all over the place, but simply showing no outward signs.
- acqq 6y ago
  > You can't have T-cells and antibodies covering every single potential surface area of every cell of every tissue in the body, so there can be places that are infected in the body even though you're totally subclinical That is exactly the mechanism how non-sterilizing protection by vaccines for respiratory diseases occurs: the cells in mucosa in the upper respiratory tract are infected every time one is exposed to the virus before the antibodies can respond. The mucosal cells shed the virus even if the infection doesn't have to result in symptoms. The viral shedding is however high enough to allow transmission to the unprotected. Note that at this very moment there are still no reports of a vaccine inducing sterilizing immunity, especially in nasal mucosa. Up to now, for the vaccines which reported the efficacy, it was by design measured and reported as protection to the symptoms of the disease. The press releases take care to mention "efficacy according to the primary study objective", where just "protection from Covid-19" (as in: from the disease with defined symptoms) was reported. Not the sterilizing immunity. (2) And, specifically for Covid-19: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31976-0/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... "Challenge studies in vaccinated primates showed reductions in pathology, symptoms, and viral load in the lower respiratory tract but failed to elicit sterilising immunity in the upper airways." (1) "These observations suggest that we cannot assume COVID-19 vaccines, even if shown to be effective in reducing severity of disease, will reduce virus transmission to a comparable degree. The notion that COVID-19-vaccine-induced population immunity will allow a return to pre-COVID-19 “normalcy” might be based on illusory assumptions." "Crucially, it will be important to communicate to policy makers and the general public that first-generation vaccines are only one tool in the overall public health response to COVID-19 and unlikely to be the ultimate solution that many expect." (Note: All cited here are the papers directly studying Covid-19, which are far more relevant in this case than a wikipedia article about what "herd immunity" were, when and if it exists.) 1) See https://www.nejm.org/doi/10.1056/NEJMoa2024671 https://www.nejm.org/doi/10.1056/NEJMoa2024671 and Figure 3 and https://www.nature.com/articles/s41586-020-2608-y https://www.nature.com/articles/s41586-020-2608-y "Viral gRNA was detected in nose swabs from all animals and no difference was found on any day between vaccinated and control animals." 2) See also my other posts here, e.g. the one which directly cites the Moderna protocol. https://news.ycombinator.com/item?id=25286838 https://news.ycombinator.com/item?id=25286838

by acqq 6y ago

gojomo 6y ago

Yes and no. These vaccines have been formally tested for their ability to protect the recipient, & there is some unquantifiable risk that they'll still get harmless-to-themselves mild infections – especially nasal/mucosal/surface infections – that can still transmit to others. But it's reasonable to also expect the following to be shown when there's more time: * The milder infection makes such infections less transmissible (in terms of duration-of-infectiousness of quantity-of-sheddding) * such superficial infections in the vaccinated don't recur often, or as they recur become ever-milder – because the nasal/mucosal surfaces themselves eventually improve their immunity. So, an extra step is required to achieve the simplified idea of 'herd immunity', but the vaccines is still one step in that direction. So it is still very much the hope & eventual aim of these vaccines to keep enough people alive, with mild easily-recovered infections, that 'herd immunity' (and thus much-lower or almost non-existent rates of infection even in the unvaccinated) is reached.

acqq 6y ago
> But it's reasonable to also expect ... - The milder infection makes such infections less transmissible (in terms of duration-of-infectiousness of quantity-of-sheddding) Neither reduced duration of infectiousness nor reduced quantity of shedding by definition protects the vulnerable. It can reduce the speed of spread, but that by definition doesn't even mean that a vaccinated person can visit their non-vaccinated or immune suppressed relative without the mask. For all we know the "quantity of shedding" has to be very low for transmission to provably not occur -- some experts estimate that a single droplet containing only 500 viruses is enough. To compare, the typical tests measure the presence of virus RNA starting with many millions in the sample and the tests do detect asymptomatic persons -- those who don't get sick now. > superficial infections in the vaccinated don't recur often From the studies of other coronaviruses it is known that infections do recur. And finally, we even know that even some percentage of people who get the vaccine become the disease later and are observably sick -- that's the difference to 100 to efficacy percentage (e.g. 5 of 100 who received the vaccine, or every 20th, if the efficacy is 95%). And we can also expect effectiveness (protection of the vaccine in the real world) to be lower than efficacy (reported from trials). In short, for all we know at the moment, the life will continue to be hard for those who don't get the vaccine and those whose immune system can't respond to the vaccine.
- gojomo 6y ago
  > Neither reduced duration of infectiousness nor reduced quantity of shedding by definition protects the vulnerable. Everything which reduces community prevalence (& case replication rates) protects the vulnerable, at least indirectly. Briefer and lesser shedding of infectious material is also likely to also contribute to milder cases among the unvaccinated - so they acquire natural-recovered immunity, both surface-mucosal and deep, over time with fewer risks to themselves & others. You are correct that simply having recently completed an initial vaccination should not give anyone confidence to immediately visit a vulnerable, unvaccinated person. After all, a surface/mucosal/sub-symptomatic infection that's still transmissible remains a possibility, especially while community infection rates are high. But 6-12 months later, when infection rates are low, and it's quite possible the vaccinated person has already been mucosally-challenged by naturally-circulating virus? At that point, the net effect of vaccines-over-time means the risk of such visits to the non-immune likely returns to the same baseline level that they had in 2018 and before, from everpresent pneumonia/flu concerns. > And we can also expect effectiveness (protection of the vaccine in the real world) to be lower than efficacy (reported from trials). It could go either way. Even in trials attempting blinding, often the vaccinated have a strong hunch (from side effects) they've received the active vaccine - and so take more risks than the placebo arm, thus causing the trial to underestimate actual protectiveness. Also, to the extent early vaccinations could be well-allocated to either most-vulnerable or most-likely-to-spread – subgroups that weren't overweighted in the trials – they could show more effectiveness in disease-prevention. And this only improves as herd immunity grows: in a tiny trial, others' vaccinations have little indirect protective effect, but as immunity rates rise in the community, there's a compounding benefit.

phobosanomaly 6y ago

Oh man, that is severely splitting hairs. You can't have T-cells and antibodies covering every single potential surface area of every cell of every tissue in the body, so there can be places that are infected in the body even though you're totally subclinical and not shedding in a meaningful sense. But such a small infection that is effectively managed by a vaccine-primed immune system is meaningless. That's like saying that a clean living-room floor isn't really clean because you can spot a speck of dust with your magnifying glass. For all intents and purposes, vaccines prevent people from contracting an infection that is clinically meaningful, and that can be spread to others in a way that leads to infection. That's herd immunity. "Herd immunity is a form of indirect protection from infectious disease that occurs when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity." https://en.wikipedia.org/wiki/Herd_immunity https://en.wikipedia.org/wiki/Herd_immunity You're making it sound like vaccinated people are walking around shedding virus all over the place, but simply showing no outward signs.

acqq 6y ago
> You can't have T-cells and antibodies covering every single potential surface area of every cell of every tissue in the body, so there can be places that are infected in the body even though you're totally subclinical That is exactly the mechanism how non-sterilizing protection by vaccines for respiratory diseases occurs: the cells in mucosa in the upper respiratory tract are infected every time one is exposed to the virus before the antibodies can respond. The mucosal cells shed the virus even if the infection doesn't have to result in symptoms. The viral shedding is however high enough to allow transmission to the unprotected. Note that at this very moment there are still no reports of a vaccine inducing sterilizing immunity, especially in nasal mucosa. Up to now, for the vaccines which reported the efficacy, it was by design measured and reported as protection to the symptoms of the disease. The press releases take care to mention "efficacy according to the primary study objective", where just "protection from Covid-19" (as in: from the disease with defined symptoms) was reported. Not the sterilizing immunity. (2) And, specifically for Covid-19: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31976-0/fulltext https://www.thelancet.com/journals/lancet/article/PIIS0140-6... "Challenge studies in vaccinated primates showed reductions in pathology, symptoms, and viral load in the lower respiratory tract but failed to elicit sterilising immunity in the upper airways." (1) "These observations suggest that we cannot assume COVID-19 vaccines, even if shown to be effective in reducing severity of disease, will reduce virus transmission to a comparable degree. The notion that COVID-19-vaccine-induced population immunity will allow a return to pre-COVID-19 “normalcy” might be based on illusory assumptions." "Crucially, it will be important to communicate to policy makers and the general public that first-generation vaccines are only one tool in the overall public health response to COVID-19 and unlikely to be the ultimate solution that many expect." (Note: All cited here are the papers directly studying Covid-19, which are far more relevant in this case than a wikipedia article about what "herd immunity" were, when and if it exists.) 1) See https://www.nejm.org/doi/10.1056/NEJMoa2024671 https://www.nejm.org/doi/10.1056/NEJMoa2024671 and Figure 3 and https://www.nature.com/articles/s41586-020-2608-y https://www.nature.com/articles/s41586-020-2608-y "Viral gRNA was detected in nose swabs from all animals and no difference was found on any day between vaccinated and control animals." 2) See also my other posts here, e.g. the one which directly cites the Moderna protocol. https://news.ycombinator.com/item?id=25286838 https://news.ycombinator.com/item?id=25286838