A quick question for our PaRDians with medical knowledge:
If the currently developed vaccines protect the vaccinated person, but do not prevent him from spreading the virus to others, how could this actually help us reach herd immunity or end the pandemic?


I'm asking because I stumbled over this point in the following article:
https://www.mercurynews.com/2020/12/14/expert-even-after-a-covid-19-vaccine-you-still-need-to-wear-a-mask/



Later in the interview, the same contradiction pops up again:


tldr: for now, we have to be cautious and assume that even those who were vaccinated can still spread the virus to others - but as soon as 70% of the population have received this vaccine which does not provide sterilizing immunity, we suddenly have herd immunity and those who cannot be vaccinated are protected either way - although the virus can still circulate among the vaccinated population (just without causing many deaths or hospitalizations) and spread from there to the unprotected segments of society?!?!

Is it me who's retarded, or does this line of reasoning not make any sense?

This post was edited by Black XistenZ on Dec 15 2020 04:10am

Just pm bazi for free medical advice
That's what i do

Hi professor Sauce here: Asymptomatic (which varies in effect from really no symptoms to something really light) people are carrying alot less quantity of the virus, and a vaccine can help help them to "finish off" the disease.

https://www.bmj.com/content/371/bmj.m4777

So yes they can contaminate others, even after a vaccine, but the incidence is super low.
In the same way the vaccine is not 100% effective anyway.

Reduce the death rate among the most vulnerable.

In red states this means easing restrictions.

In blue states this means congratulating Biden for Trump’s covid policy.

Yes, that's what I assume as well. I'm not overly concerned about this issue, it just irks me that it comes up time and time again in various articles and no one seems to notice or explain the glaring logic gap.

Still... if we assume a threshold of 70% for herd immunity and, say, 10% of vaccinated persons can still spread the virus when they're infected, then this means that 77.77% of the population have to be vaccinated to reach herd immunity. If 20% of vaccinated persons are still contagious, the effective herd immunity threshold grows to a vaccination rate of 87.5%. If 25% are still contagious, the effective threshold goes up to 93.33%.

Hence, this question of exactly how many infections spread by vaccinated persons we can expect makes a huge difference. Between ineligible groups (pregnant, chemo, immunocompromised) and anti-vaxxers, I dont think that a vaccination rate of more than about 75% is attainable.

They are less contagious than others, so the whole modelization is different.
Sure thing is we will continue to weak masks for a while. 95% success rate for vaccine: what is happening to the 5% ?

Well, that's the idea behind herd immunity: when over 70% of the population are unable to get infected or spread the infection, the virus dies out because it cant spread to a sufficient number of new hosts to sustain itself. After some time, infection levels will get so low that even the unvaccinated and the 5% where the vaccination doesnt work dont have to fear it anymore.

But that's the crux: for this approach to work, we need the vaccinations to drastically reduce the rate with which vaccinated people can spread the virus. Otherwise, harmful restrictions like social distancing or the closures of restaurants and hotels would have to be kept up for a long time, which neither our economy nor our social life can survive much longer.



I, personally, also assume that the vaccines which are currently being rolled out accomplish this reduction in infectiousness - but for now, it's an open and very critical question, and I'm quite puzzled how most of the politicians and experts touching on this point flip flop in their communication. Within one paragraph, sometimes even within one sentence, they first stress that mask wearing and physical distancing will continue to be necessary because vaccinated persons can still spread the virus, but then assume that a vaccination rate of 70% with these very vaccines will provide herd immunity.

This post was edited by Black XistenZ on Dec 15 2020 09:08am

Note that the BMJ paper is only about the Oxford vaccine, which has a way lower reported effectiveness.

The Oxford vaccine also differs from others by being viral vector based, instead of RNA based (Pfizer, Moderna).

Doesnt change the broader point, for now, the reduction in contagiousness is a concern with all vaccines, not just the oxford one.

It might not be as big of a concern with the other types of vaccines. We should still be cautious of course, but restrictions will be lowered gradually anyway.