If the COVID-19 pandemic has taught us anything, it’s that no type of virus and its consequences should be underestimated. Thus, the greatest danger is that the reservoir of these viruses is an animal. As a virus, which usually mutates and infects animals and is transmitted to humans, it can cause serious and in some cases fatal diseases, as is the case with the corona virus. Virus mutation can be caused by a variety of factors, including the genetic variability of the virus and natural selection, which allows the virus to adapt to a new human host. Thus, in recent years, an increase in zoonotic infections has been observed in recent decades. Zoonotic infections are those that are transmitted from animals to humans and can be caused by viruses, bacteria, fungi and parasites. Most infectious diseases emerging in humans have a zoonotic origin, and some examples are HIV/AIDS, Ebola, SARS, MERS and COVID-19, many of which have reactivated in recent years. Thus, one of the causes of greatest concern is the so-called airborne disease, caused by viruses that do not normally affect humans, but more and more common cases have been reported.
Influenza caused by the Asian H7N9 virus and the Asian H5N1 type of pathogenic virus are highly regarded as responsible for the majority of cases of human avian influenza virus infection in the modern world. Thus, since 1998 it has been shown that it is possible for humans to be directly infected with the influenza virus without the adaptation of pigs (as happens with influenza strains of influenza type A H5N1 and H9N2). The appearance of antigenically new types of influenza that can infect people, together with certain ecological conditions that favor genetic exchange, lead experts to consider that in a short period of time – although it is unpredictable – a new influenza virus emerges that we do not want. have immunity and could break out a pandemic that would affect the world’s population in a matter of months.
For this reason, in recent months, avian influenza has become one of the main public health concerns around the world. According to the European Center for Disease Prevention and Control (ECDC), the bird flu season between October 2021 and September 2022 was the most severe and geographically widespread ever reported in Europe.
Factors contributing to this increase include population growth, expansion of agriculture and urbanization, deforestation, and encroachment on wildlife habitats. An 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 because of the complexity of the factors involved in their transmission. However, after realizing the importance of creating a vaccine in any case, three companies (GSK, Moderna and CSL Sequirus) have recently announced that they are ready to carry out human clinical activities with their flu vaccines. How do they work, or could they prevent possible pandemic threats?
How do they work?
To confirm everyone, the report from WHO behind these movements recalled that there are vaccines against influenza A (H5N1) for human use, but the problem they pose is “they are not created.” The European Medicines Agency (EMA) gave authorization in 2014 to Baxter AG’s Pandemic Influenza Vaccine H5N1, an injectable vaccine that contains inactivated influenza virus. The vaccine contained a strain of flu called A/VietNam/1203/2004 (H5N1).
However, at the time of approval, the Pandemic Influenza Vaccine H5N1 Baxter AG vaccine had been authorized under “additional exceptions”, which means that, as a prototype vaccine, it does not yet contain the influenza virus that is responsible for the flu. to 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) have commented that they are already testing a vaccine in humans that matches the circulation of the virus. Sanofi, for its part, expressed that they are ready to start the production of a vaccine against H5N1, which they already have in general, if needed.
These human bird flu vaccines work in a similar way to the seasonal flu vaccine. These vaccines contain fragments of inactive or weakened bird flu viruses, which are introduced into the body so that the immune system recognizes them as invaders and produces antibodies against them.
Once the antibodies are produced, if a vaccinated person encounters the bird flu virus, their immune system will recognize the virus and mount a faster and more effective immune response, helping to prevent infection or reduce its spread.
However, as we have warned, these vaccines do not provide full protection against all strains of the bird flu virus, as the virus can mutate and new strains can emerge. Therefore, the effectiveness of the vaccine depends on how well the virus in the vaccine is currently circulating.
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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 because bird flu is extremely rare in humans, human vaccine trials have been limited to small studies in people who are at high risk of exposure to bird disease, such as health workers who work with infected birds.
For example, an NIH-funded clinical study of 700 healthy adults was conducted to test the H7N9 vaccine. All vaccine participants received two injections with different dosages, three weeks apart. Some doses of the vaccine are combined with an adjuvant, a substance that stimulates the production of antibodies.
The results of the study showed that those who received the vaccine with an adjuvant had a better antibody response. Even with the highest dose of non-adjuvant vaccine, the antibody response was weak. The scientists also found that a single dose of the adjuvant vaccine against the virus may be sufficient, but more research is needed to determine the duration of the antibody response.
Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), noted at the time that “although this influenza virus today is not easily spread from person to person, all new influenza viruses have the potential to evolve and cause endemic diseases or deaths.
It is also important to note that the research and development of an avian influenza vaccine for human use is a very rigorous process that involves several steps in human clinical trials and can take several years. Therefore, companies may be at different stages of the vaccine development process, and further testing and evaluation are likely to be required before the vaccine is available for use in humans. In addition, in the event that they work and we present a real risk, these vaccines remain available to countries with large resources, producing inequality in their distribution.
For this reason, in addition to the development of vaccines and potential treatments, it is important to avoid the risk of transmission of the virus from animals to humans through prevention measures, such as those surrounding the disease in animals, promoting hygienic and biosecurity practices.
