The national influenza vaccination campaign began on March 28th. The mobilization, led by the Ministry of Health, prioritizes the most vulnerable groups, such as the elderly, children, pregnant women, and people with comorbidities. The "D-Day" (vaccination day) was held on the same date, and the campaign continues until May 30th, with free vaccinations available at Basic Health Units (UBS). 

Preliminary data from 2026 indicate an increase in the circulation of respiratory viruses, including influenza. As of March 14, 14,3 cases of Severe Acute Respiratory Syndrome (SARS) had been reported in the country, with approximately 840 deaths. Among the severe cases, influenza accounts for 28,1% of the identified infections. 

Vaccination is the main way to prevent influenza and helps reduce severe cases, hospitalizations, and deaths. 

But why get this vaccine every year?  

With subtypes capable of infecting human and/or animal cells, the influenza virus multiplies by making copies of itself inside the body. 

During this process, errors can occur. Instead of perfect copies, small mistakes happen and modify characteristics of the virus, including surface proteins responsible for the virus's 'appearance' to the immune system. This is what we call mutations. While some are of little concern, others require great care and increased attention.

That's where numerous scientists from around the world come in, many of them from the Oswaldo Cruz Institute (IOC/Fioc(ruz). Like a kind of 'detectives', they dedicate themselves to investigating influenza viruses that may be 'disguised' and circulating freely.

Within the IOCThe activities are conducted by the Laboratory of Respiratory Viruses, Exanthematic Diseases, Enteroviruses and Viral Emergencies, a national reference center for the analysis of respiratory viruses. The unit is responsible for identifying, genetically characterizing, and monitoring the circulation of different influenza variants in the country. 

At the head of the Laboratory, which also acts as a Brazilian reference center for the World Health Organization's (WHO) international surveillance network, is researcher Marilda Siqueira. She and her team monitor which 'versions' of the virus are circulating in the country. 

“In a major joint effort with the Ministry of Health, the Evandro Chagas Institute, and the Adolfo Lutz Institute, we produced reports that support WHO recommendations on vaccine composition for the Northern and Southern hemispheres, based on virological and genomic analyses of hundreds of samples. In Brazil, these guidelines guide the Ministry in defining the immunization strategy and ordering the doses,” explains Siqueira.  

By connecting laboratory research, epidemiological surveillance, and global cooperation, the IOC This consolidates its position as one of the main pillars of the Brazilian response to respiratory diseases, an essential basis for the annual updating of the vaccine and for a timely response to constantly changing epidemiological scenarios.