Covd-19, does a serological test before and after the vaccine make sense to see antibodies?

Premier Draghi said he will do heterolysis because he developed low levels of antibodies after the first dose. Does such a choice make sense? And how reliable are the serological tests to verify the efficacy of vaccination?

(foto: chinaphotographer via Getty Images)

It seems done on purpose: when it comes to Covid-19 vaccinations, chaos is rampant. Always. After the mess (communicative and more) who accompanied them vaccinations under 60 with the AstraZeneca vaccine, in recent days he was the premier Mario Draghi to throw themselves into the fray, with words that mix two of the hot topics of the last few weeks: heterologous vaccinations and analysis of the antibody titer. “The heterologous works – explained the premier at a press conference – I booked myself to be a heterologous, the first AstraZeneca I did gave a low antibody response and so I am advised to do a heterologous. So how it works for me works for those under 60“. On the effectiveness ofheterologous and on the reliability of antibodies to evaluate the effect of vaccination unfortunately i doubts there are even more certainties, and the indications of the rather ambivalent experts (in addition to the fact that at the moment the option mentioned by Draghi is not available in all regions for the rest of the Italians over 60). However, let’s see what the available research says.

The Draghi affair

In the case of the Italian premier, the question is not so much linked to the safety of the second dose with a vaccine different from that of the first, as it was for many Italians under 60 who were forced to change vaccine in response to the possible dangers of thrombosis. linked to the AstraZeneca preparation. On the contrary: for Mario Draghi the use of a mix of different drugs would be preferable for maximize the immunity afforded by vaccination. After having performed the first dose the analyzes must have indicated the presence of antibodies below expectations. And this must have prompted the premier’s doctor to recommend a recall with a different vaccine. In this sense, the strategy has a rather solid, albeit still limited, scientific basis. First, viral vector vaccines, such as those of AstraZeneca e Johnson & Johnson, have a tendency to be less effective if repeated several times: our immune system does not react only to the antigen of Sars-Cov-2 conveyed by the vaccine, but also toadenovirus which acts as a vector, and when a booster is made there is a good chance that the immune response will eliminate a considerable part of these adenovirus before they reach the cells and do their job, limiting the effectiveness of the injection.

For some decades, moreover, it has been increasingly evident to the scientific community what to do prime e second doses with different vaccines (which carry the same antigen, of course) it tends to give results best compared to a vaccination homologous. Why is not yet fully understood, and probably the effect also depends on the technologies used, and the order in which the vaccines are administered. To hear the hypotheses of the experts, different vaccine technologies activate different components of ours system immune, and under the right conditions this can actually enhance the overall effect of vaccination

At the same time, vaccines different use slightly different versions ofantigenic viral and therefore mixing more vaccines can produce a more complete response, with more antibodies which are activated against the pathogen, and therefore even greater resilience against the appearance of new variants of the virus. As we said, the order of the addends is also important in heterologous vaccinations. In the case of Covid vaccines reliable data on which is the best combination are lacking (obviously, since the vaccines have been on the market for just 6 months), but some clues suggest that it is precisely the first dose with vaccine to adenovirus (like AstraZeneca) and the boost convaccino a mRna (Pfizer or Moderna) to ensure maximum effectiveness.

The dosage of antibodies

Turning to the use of test serological to verify the effectiveness of vaccination, there are no official indications to date, and the decision is left to medici e citizens, which obviously also include any costs (it must be said, content) of the exam. However, the expert opinion seems rather compact: a useless test, which offers no guarantees oneffectiveness of vaccination. It is the same opinion expressed, in America, by the Fda, which advises the population against using the dosage of antibodies, on the basis of a lack of reliable data with which to interpret a possible positive or negative result.

It is known that a small percentage of vaccinated people, regardless of the vaccine they receive, will not develop theimmunity hoped for the disease. But a lower than expected antibody level does not necessarily identify i patients at risk: immunity a Sars-Cov-2 it does not appear to be linked solely to the presence of high levels of antibodies, and not all test serological commercially available are equally effective in identifying antibodies produced in response to the vaccine.

Even on the level of basic research, there are still few certainties regarding the indicators that can help forecast the level of immunization towards Covid-19 delivered by a vaccine (or a previous infection) to a single patient. The levels of antibodies present in the blood are clearly one of the main candidates for this role, but they do not always prove effective, because immunity against a pathogen can take different roads.

The so-called immunity adaptive, the one we develop following contact with a virus or pathogen, is composed of two main elements: thehumoral immunity, linked to the activity of antibodies, is that mobile phone, in which i T lymphocytes to do the lion’s share. In the first case, the viruses circulating in the body are identified by antibodies and then neutralized. In the second, that ofcellular immunity, the process takes place within the cell infected, through the expression ofantigenic viral on their membrane and the activation of lymphocytes T, white blood cells that bind to the antigen and destroy the cell, to break the replication cycle of the virus, but which can also perform other functions, for example by activating B lymphocytes to stimulate the production of antibodies following the encounter with the pathogen.

Humoral or cellular?

Both of these mechanisms go into action to fight infections, but which will result more important depends on many factors, not least the behavior of the virus same. In the case of Sars-Cov-2 It is not yet clear which is more important to ensure immunity: some research seems to indicate that the level of antibodies neutralizzanti is a very good proxy of the security level developed by a patient; others point in the direction of an important role for T lymphocytes, both to eliminate infected cells, and as mediators that stimulate the production of new antibodies after detecting the virus. TO complicate further the situation, then, there is the fact that preventing infection is not the only goal of vaccination: if a person can contract the virus but will never develop severe forms of the disease (because the immune system is ready to take action quickly to keep the situation under control), in terms of risks individual we can probably declare ourselves satisfied. And this could be just what happens in vaccinated people they present low levels of circulating antibodies, just in case there are reservoir of B lymphocytes ready to go into action at the next encounter with the virus.

In short, the situation is complex, and it is too early to be certain about the immunological mechanisms they protect against Covid-19. Make a test serological after the vaccine to make sure it was successful then sense? Difficult to say. Except that the best thing is to rely on the instructions of your own doctor, what can be said is that currently knowing the results of the test would not change the indications for patients in a particular way, since it is still recommended to all vaccine to continue following the measures of prevention that we have learned about in the last year of the pandemic, and that in almost all Italian regions at the moment it is not possible to choose a heterologous vaccination to improve the effects of the vaccine.

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