The age at which the third dose of vaccine is being injected is decreasing. The President of the Government of Spain has just announced that people between 60 and 69 years old and health personnel will receive the third dose of vaccine to stop the next and subsequent waves.
Is this decision a precaution based on scientific evidence or a misperception of how the immune system works? I think rather the latter.
Antibodies and third dose
When a person receives the third dose, their antibody levels will increase. That is to be expected for those who responded well to the second dose and whose immune systems were activated from the memory cells created by the first dose.
The second dose produced more memory B cells (those that produce antibodies) and more memory T helper (Th) cells (those that coordinate the entire immune response including antibody production). But also, and that is the most important thing, more memory cytotoxic T lymphocytes (Tc) were generated, which are the ones that kill the cells infected by the virus.
Obviously, a third dose of vaccine will wake up all the memory lymphocytes that recognize the antigens generated by the vaccine. Consequently, they will proliferate again and produce effector cells that will produce antibodies, regulatory substances and activated Tc lymphocytes that will detect and eliminate the infected cells. Or at least it is predictable in people who respond well to vaccines , which are the majority.
The question is what happens in those who have not responded well to either the first or the second dose. The immune system is not like a nail that sinks deeper and deeper with each blow: if it does not respond to the first or second dose, it will most likely not respond to either the third or the fourth .
Efficacy based on contagion but not disease
A recent study by the Navarra Institute of Public and Labor Health has been put forward to show that vaccines are losing their effectiveness. However, the study indicates:
“The average effectiveness of the complete COVID-19 vaccination in Navarra is 69% to prevent symptomatic cases, and 91% to prevent hospital admissions for COVID-19. The effectiveness of vaccines to prevent all infections, including asymptomatic ones, is somewhat lower, 66% with a complete schedule ”.
We should keep in mind that vaccines prevent suffering from the disease in its serious version but not so much from infections .
The same organism already published another study in May 2021, a few months after starting the vaccination, in which it already indicated that having been vaccinated with the two doses reduced the possibility of infection, more that of having symptoms and much more that of need hospitalization. The panorama has changed practically nothing.
Both studies show that the double pattern continues to be effective in preventing the disease and the data on hospital admissions and deaths from the fifth wave recently passed corroborate this. Therefore, now the hospital pressure should become the most relevant and not so much the positive cases .
Immune memory, the key to protecting yourself from infection
Immune defense against respiratory viruses is complex. These viruses attack from the air we breathe. And its effect, if any, is the symptoms we associate with a cold.
These mild symptoms are nothing more than the response of the immune system trying to stop the virus and that is why we produce more mucus, we suffer a cough and some irritation or local inflammation.
In a person immunized by vaccines, the immune response occurs in the same way if he faces the virus or the vaccine. However, dealing with the virus will lead to a more general and effective response. Memory lymphocytes against vaccine antigens will also wake up. However, memory lymphocytes will also form against virus antigens not found in the vaccine, leading to a more complete and effective immune response.
A recent article published in Nature has shown that the immunological memory of past events with other coronaviruses has caused that people who have been exposed to the virus have not suffered the disease. They have not even presented a viral load detectable by PCR. These people had memory T cells against internal protein antigens of human coronaviruses that are very similar in all viruses of this type.
Another study already demonstrated in 2021 the protection by memory Tc lymphocytes in unvaccinated people . In other words, these T lymphocytes have made these people so that they have kept viruses at bay that their infection capacity has been null or almost null despite not having been specifically vaccinated against SARS-CoV-2.
In addition, in an immunized person, the response against the virus activates other responses such as the release of IgA to the mucosa . In fact, vaccines already generate a certain response in this regard. This makes the virus unable to anchor itself to cells efficiently.
Similarly, Th and Tc lymphocytes generate interferon , which blocks the proliferation of the virus. That is, the sum of immunological memory and the generation of specialized cells against the entire virus makes immunity much stronger. But even so there may be contagion and mild symptoms.
Injecting and injecting doses of vaccine simply because the cases of infection are increasing without attending to the symptoms and their severity now is a great mistake. The effective thing would be to control symptomatic cases by reinforcing primary care. Especially if we take into account that we are in the winter months in which not only SARS-CoV-2 will give rise to respiratory diseases.
Guillermo López Lluch, Professor of the Cell Biology area. Associate researcher at the Andalusian Center for Developmental Biology. Researcher in metabolism, aging and immune systems and antioxidants. Pablo de Olavide University.
This article was originally published on The Conversation. Read the original.
