nine months after the Butantan Institute submitted a request to Brazil’s National Health Surveillance Agency (Anvisa) to begin clinical research on its avian flu vaccine candidate, the agency’s analysis is still pending. This delay occurs as Brazil grapples with recent avian flu outbreaks, heightening the urgency for preventative measures.

Anvisa’s review Process

anvisa has confirmed receipt of the request and has sought additional data twice. The most recent request, issued Jan. 31, was answered by the Butantan Institute on Feb. 24. The agency stated, “Anvisa has gathered all possible efforts to give priority to strategic analysis for the country,” but a completion date for the review remains undetermined.

Recent Outbreaks in Brazil

The need for a vaccine has become more pressing following the identification of infected birds in two locations in Rio Grande do Sul. Moreover, the Ministry of Health discarded a suspicious case in a farm worker at the site of the initial outbreak. Currently, no other suspicious cases are under investigation in Brazil.

A Precautionary Measure

While human infection is rare, avian flu poses a meaningful threat. The World Health Organization (WHO) reports that from 2003 to April 10, 2025, there were 972 confirmed cases of human infections with influenza A(H5N1), including 470 deaths across 24 countries.

esper Kallás, director of the Butantan Institute, emphasizes that vaccine production is a proactive step to prepare for potential widespread transmission. Having a ready vaccine, with a platform already tested, which shows that it produces antibodies, is the goal of Butantan. He clarified, It is not to market, but to propose a strategic stock. If the ministry of Health need to trigger,Butantan will be ready to provide.

High Lethality Rate

The Butantan Institute is particularly concerned about the high transmissibility and severity of avian flu. The Pan American Health Organization (PAHO) indicates a human lethality rate of 53%, meaning more than half of those infected may die.

The vaccine under review was developed using the Influenza A variant H5N8, chosen for its high pathogenicity and potential to cause severe respiratory issues and death in humans. Preclinical tests were completed in August of last year, and a reserve lot is available for human research.

How Vaccines Are Tested

Vaccine growth involves rigorous testing, from animal studies to three phases of human clinical trials:

Preclinical Phase (Completed by Butantan):

• Animal Tests: Determines the ideal antigen and evaluates safety and protection potential.

Clinical Phase:

1. Phase 1: Study in a small group of healthy volunteers to evaluate safety, immune response, and dosage.
2. Phase 2: Involves hundreds of volunteers with the target audience profile to test safety, immune response, and formulations.
3. Phase 3: Repeats tests with thousands of volunteers, including a control group receiving a placebo, to evaluate efficacy and security on a large scale.

Global Landscape of Avian Flu Vaccines

A study in the Lancet Respiratory Medicine indicates that at least 20 licensed avian flu vaccines exist globally. These vaccines have favorable safety profiles and have been clinically evaluated in at least 32,000 people.

These vaccines are manufactured by pharmaceutical companies in the United Kingdom, Japan, South Korea, France, Australia, and China. Most use inactivated viruses produced from chicken eggs, while others are based on attenuated live viruses from cell cultures. The typical regimen involves two doses, and some are suitable for children six months and older, as well as adults 65 and older.

Common adverse reactions are generally mild to moderate, including injection site pain, fatigue, and headache, similar to those seen with seasonal flu vaccines. Despite being licensed, these vaccines are not widely used, with Finland being the only country to implement an avian influenza vaccination program for at-risk groups.

What is Avian Flu?

Avian flu, or avian influenza, is an infectious disease caused by type A influenza viruses, affecting birds and, less commonly, mammals, including humans.The H5N1 subtype is primarily responsible for recent outbreaks. Since 2022, cases have been consistently reported in countries across the Americas, including Argentina, Chile, the United States, and recently, Brazil.

Brazil confirmed two avian flu outbreaks in Rio Grande do Sul. One outbreak, considered the most concerning, occurred on a farm producing fertile eggs in Montenegro, marking the first case in commercial birds in the country.

Situation Under Control

Experts emphasize that the risk of human infection remains low. Confirmation of the virus does not indicate a situation out of control, stated Isabella Ballalai, director of the Brazilian Society of Immunizations (SBIM). On the contrary, it shows that the surveillance system is working.

Currently, there is no evidence of human-to-human transmission. Human cases are rare and typically limited to individuals with close contact with infected animals or their waste, particularly those working directly with species that transmit the virus.

The primary concern lies in the increasing spread of the virus among different animal species, which elevates the risk of mutation into a form more transmissible to humans.