If anything taught us covid-19 pandemic is not to underestimate any type of virus and its consequences. Thus, the most emphasized danger is the risk that the reservoir of these viruses is one animal. When a virus that normally affects animals mutate and is transmitted to humans, it can cause serious and, in some cases, fatal illnesses, as happened in the case of the coronavirus. Mutation of the virus can be caused by several factors, including the genetic variability of the virus and natural selection, which allows the virus to adapt to the new human host. Thus, in recent years there has been an increase zoonotic infections in the last decades. Zoonotic infections are those transmitted from animals to humans and can be caused by viruses, bacteria, fungi and parasites. Most emerging infectious diseases in humans are zoonotic in origin, and some examples are HIV/AIDS, Ebola, SARS, MERS and COVID-19, several of which have reactivated in recent years. Thus, one of the causes of greatest concern is what is known as bird flu, caused by viruses that normally do not affect humans, but increasingly common cases have been reported.

The flu caused by viruses H7N9 Asian lineage and virus H5N1 of the Asian lineage of highly pathogenic influenza, have accounted for the majority of human cases of avian influenza virus infection worldwide to date. Thus, since 1998, it has been demonstrated that there is a possibility for people to be directly infected with avian influenza viruses without the need for adaptation in pigs (as occurred with the outbreaks of influenza type A strains H5N1 and H9N2). The appearance of antigenically new strains of influenza that can infect humans, along with certain ecological conditions that favor genetic exchange, lead specialists to consider that in a short period of time – albeit unpredictable – a new flu virus for which we will not have immunity and could get out of a pandemic that would affect the world’s population in a matter of months.

For this reason, in recent months, avian flu has become a major public health concern worldwide. According to the European Center for Disease Prevention and Control (ECDC), avian flu season between October 2021 and September 2022 in Europe was the most serious and with largest geographic reach ever recorded.

O factors Contributing to this increase are human population growth, agricultural expansion and urbanization, deforestation and encroachment on wildlife habitats. The added risk is that, as we have seen, these diseases can have a significant impact on public health and the global economy, and are often difficult to control due to the complexity of the factors involved in their transmission. However, after understanding the relevance of creating vaccines in any eventuality, three companies (GSK, Moderna and CSL Sequirus) recently announced that they are ready to carry out human clinical trials of its avian flu vaccines. How do they work? Could they prevent a possible pandemic threat?

How do they work?

For everyone’s peace of mind, a report released by the WHO After these outbreaks, he recalled that there are vaccines against avian influenza A (H5N1) for human use, but the problem they pose is that “are not widely available. The European Medicines Agency (EMA) granted authorization in 2014 for Pandemic Influenza Vaccine H5N1 Baxter AG, an injectable vaccine that contains influenza viruses that have been inactivated. The vaccine contained a flu strain called A/VietNam/1203/2004 (H5N1).

However, at the time of its approval, Baxter AG Pandemic Influenza Vaccine H5N1 was licensed in ”Exceptional Circumstances”which implies that, as it is a vaccine prototype that does not yet contain the influenza virus strain responsible for the pandemic, there is no complete information on the final vaccine to face the pandemic.

Now, the executives of three of these companies (GSK, Moderna and CSL Seqirus) commented that they are already testing a vaccine that corresponds to the type of circulating virus. Sanofi, in turn, expressed that it is ready to start production of the vaccine against H5N1, which is already have in stockif necessary.

These avian flu vaccines work similarly to seasonal flu vaccines. These vaccines contain inactivated or weakened fragments of the virus avian flu, which are introduced into the body so that the immune system recognizes them as invaders and makes antibodies against them.

Once antibodies are produced, if the vaccinated person comes into contact with the avian flu virus, their immune system will recognize the virus and produce a faster and more effective immune response, helping to prevent infection or reduce its severity.

However, as we have already highlighted, these vaccines do not provide complete protection against all strains of the avian flu virus, as the virus can mutate and new strains emerge. Therefore, the effectiveness of the vaccine depends on how well the strain of virus in the vaccine matches the strain that is currently circulating.


There have been several experimental trials that have been conducted to test the effectiveness of these vaccines in humans. Of course, it should be noted that, as avian flu in humans is very rare, human trials of vaccines have been limited to small studios in people at high risk of exposure to avian influenza, such as health care workers who work with infected birds.

for example in NIH funded clinical trial recruited 700 healthy adults to test an experimental H7N9 vaccine. All participants received two injections of the vaccine at different doses, three weeks apart. Some doses of the vaccine were combined with an adjuvant, a substance that stimulates the production of antibodies.

Study results showed that those who received the vaccine with the adjuvant had a better antibody response. Even with the highest dose of the unadjuvanted vaccine, the antibody response was weak. Scientists have also discovered that a single dose of the vaccine with the adjuvant may be enough to protect against the virus, but more research is needed to determine the duration of the antibody response.

doctor Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), noted at the time that “although this flu virus currently does not spread easily from person to person, all new flu viruses have the potential to evolve and cause endemic disease or deaths”.

It is also important to note that the research and development of an avian flu vaccine for human use is a very rigorous process that involves several stages of human clinical trials and can take several years. Therefore, companies may be at different stages of their vaccine development process, and it is likely that more testing and evaluation will be needed before the vaccine is available for use in humans. Furthermore, if they work and we face a real threat, these vaccines would remain available to countries with high resources, producing inequality in their distribution.

Therefore, in addition to vaccines and the development of possible treatments, it is important to prevent the risk of virus transmission from animals to humans through preventive measures, such as surveillance of animal diseases, promotion of hygiene and biosafety practices.