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Study assesses duration of vaccine immunity to yellow fever

Paulo Schueler (Bio-manguinhos)

A question still open about yellow fever vaccine 17DD is the duration of its protection to the immunized person. The resolution of that question gains even more importance in populations living in endemic areas, and also because of the outbreak that started in 2017 and is still ongoing in Brazil. More than a theoretical debate, the answer to that question materializes in the definition of a vaccination schedule (the single dose recommended by the World Health Organization (WHO) or two doses, reinforced after 10 years, as it was recently practiced in Brazil?) and, in the case of Institute of Technology in Immunobiologicals (Bio-Manguinhos/Fiocruz), in the productive planning of the Institute.

The answer will come in the 2020s, and the first steps to take it started in June 2016, when Bio-Manguinhos began an study of duration of vaccine immunity to yellow fever in the municipality of Alhandra, countryside of Paraíba. “We expect that the results of that study will serve as a subsidy for WHO regarding the revaccination or not against yellow fever”, says Maria de Lourdes de Sousa Maia, coordinator of the Clinical Advisory (Asclin) of Bio-Manguinhos.

Lurdinha, as she is known by her colleagues, reports that the project started in Alhandra has been extended to two new locations. “In this first year of work, completed on July 4, we enrolled 802 participants for the research, now the work continues in the cities of Caporã and Conde, also in Paraíba. 

From the 808 participants who are already in the study, 572 are adults aged between 18 and 50 years old, and 236 are children. Child participation is justified: there is evidence, which may be proved by the study, that the application of the vaccine in children guarantees immunity for a smaller period than the one observed in the adult population.

In new locations, the goal is to obtain more 3 959 participants, amounting to 4 761. After being vaccinated, these people will have their blood collected in 30-45 days, 1, 4, 7 and 10 years. Data consolidated from the participants in Alhandra, for example, should start to to checked in mid-2026.

Choice and training
Due to its time of duration – a decade - the study went through a careful definition of its drawing. Even the migratory flow of “candidate locations”, for example, was studied. “We cannot lose these participants in a work that will last 10 years. Therefore, it was necessary to select locations with small migration, studying the databases of the municipalities and IBGE [Brazilian Institute of Geography and Statistics]”, explains Lurdinha.

Asked if the outbreak of yellow fever has been a criterion for mobilization of participants, the coordinator of Asclin mentioned that it has not. The municipalities were outside the area of indication for the application of the vaccine, according to the criteria of the Brazilian National Program of Immunizations (PNI). “We do not want participants to have contact with the wild virus for not to influence the data that will demonstrate how long the vaccine protects”, she says. “In a study that will continue up to 2027, it would be foolhardy to rely on a motivation for something specific, as the outbreak”, she adds. 

On August 7, it was announced the start of volunteer recruitment in the two municipalities. A week before, Asclin made an internal alignment and a training divided into two phases: the first one was a collective construction (dissertive) about the process of work that would be done, and that involved (involving) from the community health agent to the medical doctor. The second one focused on the technical training of these professionals in the research protocol in order to ensure the quality of the data.

The meeting, which brought together 69 local health professionals involved with the study, was attended by five Asclin employees. Workers who had participated in the pilot project in Alhandra has also participated. Teams of doctors, nurses, vaccinators and community health Agents trained, shared experiences and understood the importance of the work that they have started to do. After all, we may even change WHO recommendations.

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