Vaccinated with three doses have more protection against the omicron variant of the coronavirus, indicates study


Results of a study carried out with 286 volunteers during a Covid-19 outbreak reinforce the importance of the third dose of the vaccine for protection against SARS-CoV-2, including the omicron variant of the virus.

The work, published in the Journal of Medical Virology, also shows that those vaccinated with three doses had more antibodies capable of neutralizing the coronavirus than volunteers who had not completed the vaccination schedule or even those who had previously had the disease. More than 80% of those infected in the study had not taken the third dose.

“Although some of those tested previously infected could have a greater amount of antibodies that recognized the virus, those vaccinated with three doses had a better quality of antibodies, that is, that not only recognized but also effectively neutralized SARS-CoV-2”, tells Agência Fapesp Jaime Henrique Amorim, professor at the Federal University of Western Bahia (UFOB), who coordinated the study along with Luiz Mário Ramos Janini, professor at the Paulista School of Medicine at the Federal University of São Paulo (EPM-Unifesp) supported by Fapesp.

Samples were collected in the city of Barreiras, in western Bahia, during an omicron outbreak that occurred between January and March 2022. Patients who arrived at a health unit with flu-like symptoms had nasal swab samples collected. Most had blood samples collected.

The viruses present in the samples were isolated and sequenced, confirming that they were of the omicron strain. The researchers then separated serum samples from the patients’ blood to test the action of the antibodies on this variant and on the original strain from Wuhan, which gave rise to the pandemic.

“The antibodies present in the samples of those vaccinated with three doses proved capable of neutralizing not only the original strain from Wuhan, but also the omicron variant. This did not occur with those who were not vaccinated or who took one or two doses”, comments Robert Andreata Santos , who is doing a postdoctoral internship at EPM-Unifesp with a Fapesp grant and is one of the first authors of the article, along with Jéssica Pires Farias and Josilene Pinheiro, from UFOB.


Among those vaccinated who became infected during the study, only 16 had taken the third dose. The 189 who tested negative had a smaller proportion of non-vaccinated (23) than vaccinated (166), with 51 having all three doses.

The study took place at a time when few people had taken the third dose of immunizers developed against Covid-19. Those vaccinated had been immunized, for the most part, with the Coronavac or Astrazeneca vaccines in the first two doses and the so-called boost with Pfizer’s immunizer, like most Brazilians.

“As expected, we saw that the vaccine does not necessarily prevent infection. What we bring back is that those vaccinated with three doses have antibodies that even neutralize the omicron, which appeared when the vaccines currently used already existed”, explains Luís Carlos de Souza Ferreira, professor at the Institute of Biomedical Sciences at the University of São Paulo (ICB-USP) and coordinator of the Pasteur-USP Scientific Platform, another co-author of the study supported by FAPESP.

According to Ferreira, the result has repercussions for the whole world, as it shows the importance of administering additional doses of immunizers currently available to the population. In addition, the results indicate that the different combinations of vaccines applied in the country work and are able to provide protection against infection even by recent variants such as omicron.

“The data we had on the third dose were from most countries in the northern hemisphere, which were more homogeneous in the brands of vaccine used. What we have now is more relevant to the Brazilian reality”, highlights Amorim.

Preliminary results of a new analysis, recently carried out by the group in the same municipality, show that the administration of the fourth dose also had an interesting effect. The researchers observed an even lower occurrence of the disease, even among those infected.

“Apparently, the fourth dose is as important as the third. While new vaccines made especially for the new variants are not available, it is essential to maintain high levels of neutralizing antibodies in the population, which can only be achieved with additional doses”, he concludes. Andreata-Santos.

The research was also supported by Fapesp through a postdoctoral scholarship for Maria Fernanda de Castro Amarante. The study was also supported by the Coordination for the Improvement of Higher Education Personnel (Capes), the National Council for Scientific and Technological Development (CNPq), the Financier of Studies and Projects (Finep) and the Serrapilheira Institute.

The article The third vaccine dose significantly reduces susceptibility to the B.1.1.529 (Omicron) SARS-CoV-2 variant can be read here.

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