With her two doses of the covid vaccine, Marta, a healthy forty-year-old, has serious doubts about getting the third.
She has read a lot and knows that there is an immunity, cellular, that can protect her against the virus, even if the antibodies have decreased.
She believes that what is recommended for her, and for people with her characteristics, would be to have a test to see if her deeper immune system responds before being vaccinated again.
His reasoning is not entirely wrong.
More and more studies show that cellular immunity can last for months, even years, which will probably make new short-term booster doses unnecessary in the healthy population, something that the Ministry of Health does not plan for now.
But in practice it would be unfeasible to make a vaccination plan that would measure this parameter in each individual.
The tests that measure cellular immunity are carried out mainly in the most complex hospitals, which do not have the capacity to complete much more than a hundred daily diagnoses.
The campaign would take years to complete and would be meaningless from a public health standpoint.
For this reason, the decision of most developed countries has been to generalize the third doses, which have been shown to reduce the severity of the wave of the omicron variant.
A new study (not yet peer-reviewed) was published last week showing that those who have received this third shot of an RNA vaccine have a diverse repertoire of memory B cells that can respond quickly and produce antibodies capable of eliminating even new variants .
“These data help explain why a third dose of a vaccine that was not specifically designed to protect against variants is effective against serious diseases [produced by new mutations of the virus]”, indicates this research.
The La Paz University Hospital in Madrid has been carrying out cellular immunity tests for months to check how the defense system responds to the virus, regardless of whether the person has antibodies.
In the laboratory of their immunology service they collect blood samples, which they incubate for hours and then centrifuge them.
Once they separate the plasma, they pass it to a machine that stimulates this liquid with a protein from the virus and checks if it secretes another called interferon gamma.
If so, it is a sign that activated T and NK cells, two key players in the immune system, are sensitive to the coronavirus and are capable of defending themselves even if there are no antibodies in the blood.
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This technique is useful for studies on the cellular response of certain populations and to help establish vaccination guidelines.
Also for immunosuppressed people, for specific cases in which knowing this type of immunity can help choose the best treatment.
Eduardo López Granados, head of the La Paz immunology service, explains that it is performed on patients
of those who know that the antibody response will be deficient.
"It's a way of trying to see if the vaccine is generating any benefit," he says.
They are those that the Ministry of Health includes in group 7, for whom a fourth dose of the vaccine is indicated.
They are cancer patients, transplant patients, undergoing chemotherapy, with genetic immunodeficiencies, among other ailments.
“In them we know that the vaccine response is going to be partial or there is not going to be one.
We try to have something more than the detection of antibodies, which we also do, to be able to evaluate the effects of the vaccine, if they would benefit from a third, a fourth dose, ”says López Granados.
Sampling in the laboratory of La Paz.Álvaro García
This type of individualized testing can be useful, for example, to administer new drugs.
An example is Evusheld, from AstraZeneca, from which the Ministry of Health has purchased 30,000 doses.
It is a prophylactic that reduces the risk of infection for about six months in people who are not capable of generating natural immunity or who have rejected vaccines.
They are monoclonal antibodies that are given to the patient and take over the job that the immune system would normally do.
Is cellular immunity capable of predicting whether a person may suffer from a serious illness?
"Not exactly," answers Miguel González Muñoz, an immunology specialist from La Paz.
“We do not have a linear correlation in which the more response, the less hospitalizations.
At the moment we can make more qualitative estimates, categorize the patient as high or low risk, but we cannot say to any person with antibodies or cells: you are completely protected, ”he adds.
This is one of the reasons why both doctors rule out this method for the general population.
“There are many people who ask for it, even who go to private centers to do it.
But it makes no sense to apply it to everyone because neither the result is decisive nor would it be feasible from a logistical point of view”, argues López Granados.
The results of the cell test, in addition, give indications of the ability to generate antibodies, but they are not capable of measuring all the defense parameters of the organism.
“The cellular response is very varied and there are two types that we are not measuring.
In the end, it is the set of all these responses that determines in each person what happens in a real situation of infection”, emphasizes this doctor.
Criticism of generalized booster doses
The Spanish Society of Immunology has been critical of the indiscriminate application of the third dose to the entire population.
Although she is in favor of administering it to older people and those with certain problems, she believes that the treatment should be more individualized.
Not with specific tests for each citizen, but by fine-tuning more in population cohorts thanks to tests like these.
This path to more precision medicine clashes with most public health experts, who generally favor immunizing as many of the population as possible, which has been shown to translate into fewer hospitalizations and deaths.
In several studies, such as the one published last week, the third dose has been shown to improve the immune response even against omicron.
What some immunologists are asking for is to further refine the knowledge in order to prick only the population that is really most susceptible to getting sick from the coronavirus.
They fear that a succession of vaccines and infections could end up sapping the immune system.
“With three doses of the vaccine this does not happen, but if you are continuously stimulating the cells you can exhaust their life cycle.
I believe that we must flee from both extremes.
In other words, if you get vaccinated three or four times you will not end up not responding or generating an inflammatory response, something that has been shown, nor should you be continuously vaccinating indiscriminately, ”says López Granados.
The booster dose campaign in Spain is far from achieving the acceptance that the first two had.
If in this first phase it was one of the world leaders, with the third dose only half of the population has been vaccinated, only slightly above the European Union average, and well below others such as Chile (68%) , Denmark (62%) or Italy (60%), according to data from the Our World in Data repository.
The vast majority of the population over 60 years of age (92%), the most susceptible to becoming seriously ill from the coronavirus and for whom this injection is most useful, is protected with this reinforcement.
But as age decreases, this percentage decreases.
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