Except that antibodies don’t tell the whole story. They may wane after a while, but the immune system is primed to fight off the virus at the next infection thanks to memory B cells and T cells.
Unfortunately, T-cell tests are not available in Europe, and apparently not reliable in the US. Which confirms the original point: there seems to be little interest in detecting previous infections.
Many people who have been infected with SARS-CoV-2 will probably make antibodies against the virus for most of their lives. So suggest researchers who have identified long-lived antibody-producing cells in the bone marrow of people who have recovered from COVID-191.
The study provides evidence that immunity triggered by SARS-CoV-2 infection will be extraordinarily long-lasting. Adding to the good news, “the implications are that vaccines will have the same durable effect”, says Menno van Zelm, an immunologist at Monash University in Melbourne, Australia.
The natural immune protection that develops after a SARS-CoV-2 infection offers considerably more of a shield against the Delta variant of the pandemic coronavirus than two doses of the Pfizer-BioNTech vaccine, according to a large Israeli study that some scientists wish came with a “Don’t try this at home” label.
Which means that testing is really undependable. Probably better to vaccinate everyone, because our prediction of the immunity of people who have been vaccinated is a lot more reliable.
From an economic perspective, if the cost of the vaccine is less than the cost of the test, you just use the vaccine. "Natural immunity" makes sense as an objection if the individual had a recorded earlier infection, but administering 300M pre-infection tests and 200M vaccines is likely to be less efficient than just administering 300M vaccines. The more sophisticated of a test you demand, the stronger this argument becomes.
You would just be administering a cure, without having an actual diagnosis, which is by definition more wasteful.
Particularly when natural immunity comes for "free" and apparently works better, at that point insisting on vaccines for everybody is just completely nonsensical.
Rather shift resources to testing to get costs for that down, which is more work, but also doesn't come with the risk of later discovering "Oops, this vaccine that made people filthy rich turned out to have some nasty long-term side-effects!".
Which is also a very real possibility, considering they've been developed and approved in record time with the population at large acting as subjects for the first non-clinical trials.
A vaccine is an innoculation and prophylactic, not a cure.
The prophylactic costs less than the diagnostic. It has negligible risk of harm. It's a determinable and unambiguous event, unlike trying to verify a possible infection and sustained immune response.
The obvious rational policy decision for public health is to mandate the vaccine for everyone.
Those not previously infected gain immunity. Those previously infected ... either get a not-strictly-necessary injection, or far more likely, a useful booster.
And the administration, diagnostic, and monitoring costs are far lower.
I think Canada accepts positive covid tests as proof of prior infection, and many people already have those tests done and just sitting in their email.
Canada doesn't have a national health care system, this is managed by each provinces.
Quebec is the only province that will let you get only 1 dose of the vaccine, instead of 2, if you were previously infected. With that 1 dose, that's enough to have access to the vaccine passport.
But there are absolutely no places in Canada that accepts prior infection as being fully vaccinated.
I mean, that's fine, but it's not what the parent was asking for. It seemed that they were implying we needed to catch every pre-infection, and the lack of development of highly sensitive tests for pre-infection was evidence of some negligence. I was arguing against developing "T-cell tests" for prior COVID infection.
My comment was not intended to be an argument against any testing for pre-infection; I think the rationale for that is pretty solid, but I think that the regulatory establishment needs to be prepared to inform people that they might not be able to prove their previous infection and in that case they should get vaccinated.
Can you be sure the temporary side effects (caused by the engagement of the immune system) wouldn't be diminished for people with existing immunity? It might not be as much of a concern.
I believe one of the major studies that found that natural immunity was better than the Pfizer shot alone also found that natural immunity plus the shot was better still.
Unfortunately, T-cell tests are not available in Europe, and apparently not reliable in the US. Which confirms the original point: there seems to be little interest in detecting previous infections.