“Now that you have been vaccinated, are you immunized? Take a test to find out ”.
This is the message that different laboratories are launching to give a second life to antibody tests. In this way they invite us to “measure” our immunity to the virus after the vaccine. Or to clear the doubt: will I have passed the Covid and can I not get vaccinated?
There are even laboratories that for their publicity resorted to a disturbing “Have you been vaccinated well?” that irritated the nursing professionals. “Do not sow doubts about vaccination to sell your tests, much less put the focus on the act of vaccination or those who carry it out, ” requested the General Council of Nursing.
Antibody tests, also known as serological tests or rapid tests (not to be confused with antigen tests), are used to detect the antibodies generated by our immune system to neutralize SARS-CoV-2 after having passed the infection, or those generated in response to vaccination.
Although they have some usefulness in seroepidemiological studies, such as the ENECOVID study developed in Spain, and in some other situation, their interest in active infection is very limited. Despite this, in Spain they had a first (and controversial) life during the past year when they were used – let us say in an unorthodox way – by some municipalities and some autonomous communities. Something similar happened after the authorization at the end of 2020 for its realization in community pharmacies.
Surprisingly, vaccination has given them a second life, no less unnecessary than the first.
Why it is unnecessary (and counterproductive) to do serological tests to verify if we are immunized
There are several arguments for dispensing with serological tests in vaccinated people:
The immune response is complex, and antibodies are only part of that response. A very robust immunity against SARS-CoV-2 can be maintained by having undetectable antibodies (especially with rapid tests) or with very low titers. In fact, antibody titers will decline over time while immune protection is maintained thanks to T lymphocytes, responsible for cellular immunity.
The opposite situation is also possible. Although antibodies are an indicator of immune response, having detectable antibodies does not exclude the possibility of infection, as we are seeing these days with infections in vaccinated (mostly mild). The effectiveness of vaccines, still extraordinarily high, is not absolute. And they behave better against the development of serious pictures than against infection.
At this time, we do not have studies that establish the correlation and the “cut-off points” that imply protection based on the titers and types of antibodies against SARS-CoV-2. Studies are under way in this regard, but with the intention of finding parameters that can serve to shorten the duration of clinical trials rather than for individual use.
Nor do we have a widely accepted management alternative of what to do with people with low or undetectable titles. In some groups of patients with a poorer general immune response (immunosuppressed, transplanted, and others) it might be reasonable to use a third dose, but – at least for the moment and with the exception mentioned – we have many first and second doses to administer (also in the poorest countries) rather than thinking about the third .
The protection offered by vaccines is not based only on reducing the individual risk of vaccinated people. That our environment is vaccinated is essential for individual protection and with our vaccination we contribute to the protection of all. It is solidarity and it is self-interest. Whatever “our” antibodies count, our protection also depends, and a lot, on the antibodies of our neighbors.
There are many rapid antibody tests (about 50 approved in the United States), although none validated or licensed to assess the immune response to vaccination. For this reason, the health authorities advise against its use for this purpose. These tests vary markedly in their diagnostic performance and can result in different proportions of false positives and false negatives.
Not all commercialized tests detect the antibodies generated by vaccination (which only generates antibodies against the coronavirus spike, the so-called anti-S). Some only detect antibodies against the virus capsid (anti-N) and give negative results in vaccinated people.
So how do we know that vaccines work?
We know that vaccines are effective against severe cases of Covid from clinical trials that led to their authorization by drug agencies. Several subsequent studies, with real life data in millions of people, have confirmed these results and have shown that, additionally, vaccines significantly reduce asymptomatic and mild cases and transmission.
In Spain, a study by the PROVAVAC program of the Generalitat Valenciana (not yet published, but with the main results presented) showed that 98.7% of a representative sample of almost 900 people residing in centers for the elderly (a priori, a group with less immune responsiveness) had detectable antibodies 3 months after the full regimen. Somewhat more in vaccinated people who had previously suffered from Covid (99.6%) but practically indistinguishable from those only vaccinated (98.3%). And a good part of the remaining 1.3% showed a cellular immune response.
It is not mandatory to also mess with serological tests
Throughout the pandemic – in Spain, but also in many other countries – we have tangled, discussed and created uncertainty with many things. From masks to mobility restrictions, from antigen tests to age cuts for the use of each vaccine, from isolates from close contacts to the adverse effects of immunization.
Although entanglement is already more a tradition than a custom, it is not mandatory to do it with serological tests as well. The least desirable at this time is that healthy and vaccinated people go to their doctors to demand an absurd test (which their doctors reasonably will not want to prescribe) or because a test has been performed (not always reliable and almost never interpretable in terms of immune protection ) and has tested negative.
It is unnecessary, counterproductive and, in the midst of a rebound in cases and high pressure in primary care, it is the worst time to get confused. For this time, let’s heed the recommendation of Dr. Fauci, the presidential advisor on Covid matters in the United States, who in recent statements to Insider said emphatically that he did not plan to waste his time taking an antibody test … and that no one should do it.
Let’s not waste our money. Neither does our time. Neither does that of health professionals.
Salvador Peiró, Researcher, Health Services Research Area, FISABIO SALUD PÚBLICA, Fisabio
This article was originally published on The Conversation. Read the original.
