The problem is that none of the vaccine candidates evaluated so far do not necessarily provide sterilizing immunity in many or even most people, e.g. stop the virus from propagating and disable infected cells quickly. It is clear that the vaccines provide some level of protection short of this, because they have shown dramatic reductions in mortality, but whether that translates into a significant reduction in infectivity is unknown.
Part of the problem of detecting infectiousness is that viruses are not biologically active outside of the body, and while PCR tests can demonstrate the presence of specific viral genomic material they cannot distinguish between active viruses and RNA fragments. The only way to really determine if someone is shedding active virus is by running a plaque assay, and for this virus that requires doing so in a Biosafety Level 3 (BSL3) lab.
Antibody tests will demonstrate if you have developed an effective immune response, which very probably means you’ll have good protection against serious effects even if the virus manages to infect tissues and replicate. Whether this means that the virus can’t get enough of a foothold to replicate sufficiently for someone to shed active virus is still unknown, which is why health authorities are cautioning people who have had the vaccine to still wear masks, maintain distance, et cetera, until a large percentage of the population has been vaccinated.
And there is still the potential that one of the several variants currently identified, or others that may develop in the coming months, could be sufficiently resistant to the immune response from the current vaccines to be capable of infecting and spreading, and the longer there is a large population of people who are not inoculated the more likely that could occur, as could spillback from animal reservoirs, so a continued need for surveillance and maintaining the infrastructure do modify, test, produce, and distribute more vaccines is crucial to being able to safely open everything back up.
Stranger
Thanks, Stranger. I can always count on you for sound, thorough explanations. I’m not seeing that antibody testing post-vaccination is a common practice. I’d guess most people think 90-95% means they’re protected. Having been on the wrong side of long medical odds a few times, I’m a bit wary. When I’m eventually able to get vaccinated, I’ll have to think about getting tested a few weeks after the second dose.
Rapid at-home tests are being developed which are supposed to tell people whether or not they are contagious. This article does not go into detail about the science behind it, but it sounds to me like it would be able to equally tell whether a vaccinated or non-vaccinated person is shedding infectious particles:
Rapid at-home COVID-19 test developed at KU moves closer to production
I am very interested in this as I will soon have a baby that will not be able to be vaccinated for an unknown amount of time.
I have a related question that I hope is OK to add to this one. Are there other viruses where the vaccine only protects the vaccinated? That is, where someone who is vaccinated may still infect others?
ETA: I’m not saying that is the case with this virus, but I’m hearing that it may be the case – that is, there’s no evidence either way.
Note that even in the cases where vaccination did not prevent infection, (or rather, prevent overt signs and symptoms of COVID-19 because neither the Moderna or Pfizer trials comprehensively performed rtPCR tests on the entire population), it appears to have significantly reduced severe morbidity and mortality in the vaccinated population as compared to the baseline unvaccinated population. The testing didn’t include people with severe comorbidities or the elderly so there is still uncertainty about the efficacy in those populations but the vaccine clearly offers a measure of protection even if it doesn’t prevent infection.
Note that antibodies developed by the vaccine will eventually fade but memory B cells will hopefully retain the ability to reactivate the adaptive immune system to produce neutralizing T lymphocytes (so-called “helper” and “cytotoxic” T-cells). So even after IgM and IgG antibodies disappear from blood, the ability to attack the pathogen hopefully still remains, as does the innate immune response.
Stranger
I think the flu shot fits. Sometimes the flu vaccine just makes a flu case less severe, but you still have flu (and therefore could transmit it).
You have to be careful looking at this because the gold standard for “not infectious” is sterilization inmunity, which basically means the vaccine doesn’t allow any detectable virus to exist in you. The better question is how much less infectious it makes you.
I’m kind of conflating “be infected” and “be infectious” in these last couple posts. It’s legitimate in many ways.
Thanks, @FigNorton!
On the flu shot, I’m not sure if that fits – my understanding is that there are lots of flu variants around, so you might not even be vaccinated against the one you get sick with, though it can still reduce the severity of the disease. Anyway, it’s a minor point either way.
I have a question too. I’m glad we’ve vaccinating people, truly, but does the fact that a lot of people have been given the vaccine and more will soon mean that the window to test people with newly developed and allegedly much more accurate tests for antibodies like the ones announced within the past week or so mean that our window for finding past, unreported infections is closing? I mean, once a significant portion of people have gotten the vaccine we’ll never be able to accurately figure out if 90% of people who had Covid were tested or if 10% were, right?
Being vaccinated does not eliminate infection. But if you already have an immune system response ready to kick in immediately due to being vaccinated. Your viral load will not get too high. You will eliminate the virus internally quicker. So you will not be spewing out as many viral components. You will be less likely to infect others. But it can be possible. This is the case for most things that we vaccinate against. It does not mean it does not infect you. But your body deals with it and kills it very quickly. Lessens the chances of passing it on greatly.
Probably. Can you link to information on the new tests?
I believe these are 3 new different tests
Canadian researchers develop faster, more accurate COVID-19 antibody test
Are COVID antibody tests accurate? Local lab says its up to 99.9% reliable
From the third link:
"The test is a breakthrough because it examines more viral antigens than most other antibody tests and therefore can learn a lot more about a patient with symptoms, said Dr. Daniel Linseman, associate director of the Knoebel Institute for Healthy Aging.
“Most serology tests that have been approved by the FDA so far test for only one or two viral antigens, whereas this test will test for 12 different viral antigens,” Linseman said.
In spite of the headline, that’s an antigen test, not an antibody test. It directly tests for the presence of COVID-19, it doesn’t test for the presence of immunity, it’s not affected by vaccination except in the previous couple of days.
The other two seem to be antibody tests.
An antibody test will be defeated by vaccination if it tests for the same antibody that vaccination produces. I would expect a de-activated virus vaccination to probably produce the same antibodies that the virus does, and to defeat a generic antibody test.
The TB skin test is an example that does not differentiate between past infection and past vaccination.
The mRNA vaccines were quickest to be developed, and fasted to be produced. It is my understanding that they each code for one particular antigen, and the reaction produces only one particular antibody. They will defeat an antibody test that tests only using that antigen (that detects only antibodies for that antigen). It should be possible to develop a different antibody test, but it may not be as good. You would expect that, as with TB, laboratory tests will still be able to notice that this is a narrow vaccine-specific antibody response. It may be made more difficult by the range of vaccinations, or by other kinds of non-mRNA vaccinations.
The two approved mRNA vaccines both code for the spike protein (an antigen) slightly modified to hold it “open”, to promote antibodies against the active bit. The spike has a few different surfaces that antibodies form to attack, though. So I think you’d call it a single antigen, but several antibodies.