Leading scientists warn that influenza is the pathogen most likely to spark a new pandemic soon. An international survey presented at the ESCMID Global Congress (formerly ECCMID) in Spain, indicated that 57% of senior disease experts believe a strain of the flu virus will be the cause of the next global outbreak of a deadly infectious illness.
The belief that influenza poses the greatest pandemic threat is supported by extensive research demonstrating its constant evolution and mutation, according to Jon Salmanton-García from Cologne University, who led the study.
What do the experts think?
“Each winter, influenza appears,” he noted. “These outbreaks can be seen as small pandemics. They are relatively controlled because the strains causing them aren’t virulent enough – yet this might not always be the case.”
The survey, which gathered insights from 187 senior scientists, will be detailed at the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) congress in Barcelona next weekend.
Following influenza, 21% of experts in the study believe the next pandemic may be caused by an unknown virus, referred to as Disease X. This hypothetical pathogen could emerge unexpectedly, similar to how the SARS-CoV-2 virus, which causes COVID-19, appeared in 2019. Additionally, 15% of the scientists surveyed still consider Sars-CoV-2 a potential pandemic threat in the near future.
Other pathogens like the Lassa, Nipah, Ebola, and Zika viruses were deemed serious global threats by only 1% to 2% of respondents. “Influenza was overwhelmingly considered the top pandemic threat by a large majority of scientists worldwide,” Salmanton-García added.
Selecting seasonal influenza vaccine compositions
Annual seasonal influenza epidemics result in up to 650,000 deaths globally. These deaths primarily affect individuals at higher risk of severe disease, including older adults, people with chronic heart or lung conditions, children under five, and pregnant women. The seasonal flu vaccine is a safe and effective measure to reduce the severity of infections.
To tailor the vaccine to circulating variants, the WHO organises biannual consultations with an advisory group of experts from WHO collaborating centres and WHO Essential Regulatory Laboratories. These experts analyse influenza virus surveillance data generated by the Global Influenza Surveillance and Response System (GISRS). The recommendations they issue are used by national vaccine regulatory agencies and pharmaceutical companies to develop, produce, and license influenza vaccines for the upcoming season.
Experts also analyze viruses circulating in animal populations to develop candidate vaccine viruses that could be essential in combating a future pandemic.
“One fascinating aspect of flu is its continuous evolution, allowing it to evade prior immunity we might have to specific flu viruses,” explains Nicola Lewis, Director of the Worldwide Influenza Centre at the Francis Crick Institute in London, United Kingdom.
“Flu viruses can also undergo what we call re-assortment. This occurs when two different flu viruses infect a person or a pig simultaneously. They shuffle their genetic material, resulting in a progeny flu virus that is different.”
Pigs serve as ideal mixing vessels for flu mutation since they can contract influenza from both birds and humans. Periodically, viruses from specific animal populations spill over into other animal populations or humans, where they can cause severe illness. While these incidents sometimes result in isolated infections, they hold the potential to spark a pandemic.
“Flu viruses are constantly changing, and our job, as collaborating centres supported by the extensive work of the national influenza centres, is to understand these changes. The seasonal flu vaccine remains a crucial tool in protecting the human population.” added Nicole.
Why is it a potential pandemic threat?
Highly pathogenic avian influenza (bird flu) has garnered significant attention due to its recent rapid evolution and its ongoing detection in cattle in the United States. This virus is often lethal to domestic poultry, though it has not yet proven easily transmissible to humans. Since 2020, various strains of the virus have spread globally via wild bird hosts, affecting regions across Eurasia, Africa, North and South America, and even Antarctica.
In addition to killing millions of wild and domesticated birds, including poultry raised for human consumption, highly pathogenic avian influenza has shown the ability to infect mammals such as tigers, foxes, mink, and fur seals. Infections in mammals are particularly concerning as they could lead to mutations that enhance the risk of mammal-to-mammal transmission and potential spread to humans.
“We have never encountered a situation like this with a highly pathogenic H5N1 virus before. If you had asked me in 2019, I would not have envisioned this scenario for bird flu,” remarks Nicola.
Nicola emphasises that frameworks such as the Global Influenza Surveillance and Response System (GISRS), which are crucial for global pandemic preparedness, rely on trusting, collaborative partnerships and the sharing of near real-time information.
In conclusion
The prospect of a flu pandemic is concerning, though scientists note that vaccines for many strains, including H5N1, have already been developed. “If an avian flu pandemic occurred, it would still be a significant logistical challenge to produce vaccines at the necessary scale and speed. However, we are much better prepared now than we were during the COVID-19 pandemic when a vaccine had to be developed from scratch,” stated virologist Ed Hutchinson, of Glasgow University, in an article for The Guardian.
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