Serological tests, which detect antibodies in the body from the blood, are not recommended by infectologists for three reasons:
1) the immunological response intended with the vaccine is not only of antibodies, it also involves T-cells – not detectable in this type of test;
2) the neutralizing antibodies that are developed from vaccination are not measurable by the tests available in the commercial network of laboratories and
3) there are still no defined parameters in relation to the amount of antibodies that can determine whether there is immunity to viruses.
Infectologist Ana Helena Germoglio explains that post-vaccine serological tests can even give a “clue” about the production of antibodies – if the rates of IgG and IgM have gone up. However, the expert does not recommend that the tests be done for this purpose because the information is by no means secure.
“People need to understand that these tests were not created for this purpose, so their result is not reliable information about the effect of the vaccine or the immunity produced. The number of false positives and false negatives is high ”, says the doctor.
Infectologist Werciley Júnior, from the Santa Lúcia group, adds that “diagnoses of immunity” based on blood tests can produce a false sense of security or unnecessary panic. “Even if the test detects an increase in antibodies, the person should not consider himself immunized, as we have no defined parameters to guarantee this immunity”, he says.
On the contrary, if the test does not detect higher rates of antibodies, it does not mean that the vaccine did not work. “The immune response involves several mechanisms and varies from person to person, so there is no way to diagnose immunity by a blood test”, says the doctor.
The Brazilian Society of Immunizations (SBIm) recently took a stand with a technical note on the subject. “The complexity of post-vaccination immunity or even after natural disease, however, does not support the performance of the tests, as the results do not reflect the individual protection situation”, affirm the entity’s experts in a text published on March 25.
Experts recommend that, even after vaccination, people maintain basic protection measures: wearing masks, hand hygiene and social distance.
At the current moment of the pandemic in the country – with wide circulation of variants and few people vaccinated -, there is still a risk that the immunized ones will be asymptomatic transmitters of the virus. And, in addition, the vaccines applied in the country still do not provide 100% protection against Covid-19, they are effective against the development of the most serious cases of the disease.
See in the gallery how vaccines against Covid-19 work:
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