Let me try to find yet another way to explain the issue with mass vaccination campaigns.
First, do never ask yourself (or others!) who spreads more, the ‘healthy’ vaccinees or the ‘healthy’ unvaccinated as you shouldn’t care too much about the viral load you get exposed to, as long as it originates from a healthy person. What’s currently important from a personal health viewpoint is ‘how susceptible you are to contracting the disease due to a more infectious variant?’ That has more to do with your immune status:
So, if you’re a vaccinee, the higher your vaccinal anti-S(pike) antibody (Ab) titer, the better you’re protected against C-19 disease caused by the currently circulating, more infectious variants, in particular by the Delta variant (so, 2 shots protect better than one).
If you enjoy naturally acquired immunity, there isn’t even any need to care about your Ab titer at all. You may get some mild symptoms if you happen to get infected while your Ab titer is low but, as soon as your immune memory gets the wake-up call, it’ll provide you with very potent antibodies that can deal more effectively with all of the variants – even at relatively low concentration – than vaccinal anti-S Abs do.
So now, what if you’re not vaccinated at all and you don’t have naturally acquired Abs either (so, in other words, you didn’t contract C-19 disease before)? In that case, the lower your anti-S Ab titer, the better! You may, indeed, have anti-S-specific Abs that are short-lived and result from previous, asymptomatic infection. Although those have low affinity for the Sars-CoV-2 spike (S) protein (as asymptomatic infection doesn’t suffice to prime your Ab-producing B cells properly), they’re capable of suppressing variant-nonspecific innate Abs, which have an even lower affinity for the spike (S) protein (that’s why they can be outcompeted by anti-S-specific Abs) and normally bind to coronavirus particles through multivalent interactions.
But what about the public health impact of the vaccines? So, now we’re talking about mass vaccination. Let’s first keep in mind that the likelihood for vaccinated and unvaccinated individuals to become infected with the Delta variant is now about the same. However, infection with more infectious variants in vaccinees can be problematic from a public health viewpoint when occurring on a background of high vaccine coverage rates (due to mass vaccination!). This is because high vaccine coverage rates i) favor propagation of more infectious variants, which poses an indirect threat to the unvaccinated and ii) eventually causes growing resistance to S-specific antibodies. In contrast, there is no such public health risk associated with Sars-CoV-2 infection in the unvaccinated. However, the latter are exposed to a personal health risk when they get re-infected shortly after a previous exposure to Sars-CoV-2 (which is more likely to occur when highly infectious variants such as the Delta variant are circulating). Disease caused by fast re-exposure of an unvaccinated person to a highly infectious variant will usually be milder in young and healthy individuals (e.g., healthy children) than in older age groups. Recovery from disease will always result in life-long immunity and thereby contribute to herd immunity.
Conclusion: The debate about who shed more and who shed less is scientifically irrelevant as long as we’re talking about healthy people. If you didn’t contract the disease in the past and you didn’t get vaccinated, you’re now at relatively high risk of contracting the disease (because there is a relatively high likelihood that you’ll get re-infected shortly after your previous infection simply because dominance of the highly infectious Delta variant makes it more likely). Your infection has no detrimental public health consequence as your immune system will not exert selective immune pressure on the spike protein, regardless of whether or not you get the disease.
Now, if you didn’t contract Covid-19 in the past and you got fully vaccinated, you will (for now) be protected against (severe) disease. However, if your vaccination occurs as part of a mass vaccination campaign, you, together with all other vaccinees, will exert suboptimal immune selection pressure on viral infectiousness. This will expedite the further expansion of circulating, more infectious variants and eventually lead to dominant circulation of an immune escape variant that is both highly infectious and S-Ab-resistant. Although you will still have taken care of your personal health, the fact that you’re part of a ‘universal’ vaccination effort will have a detrimental impact on public health in that it first threatens the unvaccinated but ultimately also all of the vaccinated people (as explained under i) and ii) above). That’s why I am always warning about snapshots and short-term perspectives. It’s exactly this attitude that is now motivating our health authorities and politicians to rapidly expand mass vaccination campaigns to youngsters and children. If one thinks pandemic- and public health-‘wise’, we should of course do whatever we can to not further promote breeding of highly infectious variants such as to not allow them to become resistant to S-specific Abs (an evolution which is now well on its way!). This is to say that extending mass vaccination to our children is not going to help anybody. We need to protect them as much as we can through measures other to vaccinate them with any of the current C-19 vaccines (see previous contributions of mine). They’re having the best chances to resist the high infectious pressure from the Delta variant. When asymptomatically infected, they are key to diminishing the infection rate from more infectious variants, whereas their recovery from symptomatic infection is key to building herd immunity!
I hope people start to see that no single healthy individual should be considered more of an infectious threat than another and that there is no scientific rationale whatsoever for any individual, whether vaccinated or not, to discriminate against contacts with any healthy vaccinated or unvaccinated person. THE one and only big issue is the scale of this vaccination campaign. None of the current Covid-19 vaccines can live up to the challenge of controlling a pandemic of a highly mutable virus, let alone when variants are already predominantly circulating. When vaccines work, but are not perfect, and you massively deploy them in the heat of a furious (Delta!) pandemic, then you’re in really deep trouble.